Southampton wasted the chance to return to the top of the Championship as goals from David Nugent and Matt Mills gave Leicester victory at St Mary's.
Saints were two down after 26 minutes, former Portsmouth striker Nugent opening the scoring by cutting in from the left to curl home a 20-yard shot.
Former Southampton defender Mills added a second with a header from six yards.
Dean Hammond headed Southampton's best chance across goal, while at the other end Paul Konchesky struck a post.
It was a second successive home defeat for Southampton, who lost to Bristol City on 30 December.
Their next home league game on 31 January takes on added importance as it is against third-placed Cardiff, who are currently only one point behind them.
For Leicester, managed by former Saints boss Nigel Pearson, it was the completion of a double over the south coast side, following their 3-2 home success in August.
Both sides had early chances at St Mary's, last week's FA Cup hat-trick hero Jermaine Beckford firing wide from 12 yards inside a minute for Leicester, and David Connolly also off target for the Saints.
A 20-yard Connolly strike was comfortably saved by Kasper Schmeichel and, after Nugent's impressive ninth goal of the season, the Saints struggled to find a way back into the match.
DID YOU KNOW?
Saints have lost more home league games within the last month than in the whole of 2011
When Sean St. Ledger picked up the ball on the left and delivered an inch-perfect cross for Mills to head home his first goal for Leicester it proved too much for the home side to recover from.
Jack Cork fired over when well placed four minutes before the break after good work from Morgan Schneiderlin but, soon after the resumption, Nugent came close to a third for the visitors, sending another curling effort just wide.
Schmeichel kept out Hammond's far-post header, while Konchesky was unfortunate to see his free-kick come back off the woodwork and roll to safety.
In the closing stages Saints subtitute Lee Holmes fired wide with a sorry effort that summed up the home team's evening.
Southampton manager Nigel Adkins:
"We were up against it tonight. As I have said on many occasions, when things aren't going right that's when you find out about people and we have found out about all of us tonight in certain ways.
"Emotions are quite high at the moment but we will reflect on it in the cold light of day. We need to work very hard to keep driving this club forward.
"We have to grind out performances and tonight wasn't good enough, we know that.
"We will reflect on the performance and reflect on the result, we still have a long way to go and we have to work very hard and stick together."
Leicester boss Nigel Pearson:
"I am very pleased for the players. They have put a lot in to the game tonight and they have got what they deserved.
"It is all well and good having talented players but whatever level you play at you must always work harder than the opposition and the work ethic really was exceptional.
"This is a long way to come for us all and for the supporters especially it is a great result.
"They made a tremendous noise and backed the players from the start right until the finish."
- 01 Davis
- 03 Harding
- 13 Fox
- 16 Martin
- 26 Hooiveld (Richardson - 65' )
- 04 Schneiderlin
- 08 Cork
- 10 Guly
- 14 Hammond (De Ridder - 56' )
- 27 Falque (Holmes - 56' )
- 22 Connolly
- 21 Bialkowski
- 02 Richardson
- 28 Reeves
- 24 Holmes
- 33 De Ridder
- 01 Schmeichel
- 02 Peltier
- 03 Konchesky Booked
- 05 Mills
- 12 St. Ledger
- 11 Dyer
- 19 Wellens
- 23 Danns
- 07 Gallagher (Drinkwater - 42' )
- 20 Beckford (Delfouneso - 75' )
- 35 Nugent Booked (Howard - 87' )
- 25 Logan
- 30 Kennedy
- 16 Drinkwater
- 09 Howard
- 24 Delfouneso
Live Text Commentary
Full Time The referee ends the match.90:00 +2:53
Free kick awarded for an unfair challenge on Daniel Fox by Nathan Delfouneso. Direct free kick taken by Kelvin Davis.90:00 +2:26
David Connolly gives away a free kick for an unfair challenge on Matt Mills. Free kick taken by Kasper Schmeichel.90:00 +2:03
The official flags Daniel Drinkwater offside. Indirect free kick taken by Kelvin Davis.90:00 +1:16
Short corner taken by Neil Danns.89:28
Steve De Ridder fouled by Neil Danns, the ref awards a free kick. Free kick crossed left-footed by Daniel Fox from right channel, Kasper Schmeichel makes a comfortable save.88:26
The ball is crossed by Lee Holmes, Steve De Ridder has a headed effort at goal from close in which goes wide right of the goal.86:32 Substitution
Substitution Steve Howard comes on in place of David Nugent.85:37
Richie Wellens is adjudged to have handled the ball. Free kick taken by Jack Cork.84:53
David Connolly is ruled offside. Kasper Schmeichel restarts play with the free kick.84:03
Nathan Delfouneso challenges Jack Cork unfairly and gives away a free kick. Frazer Richardson takes the direct free kick.83:34
Neil Danns sends in a cross, save made by Kelvin Davis.82:41
Lee Holmes produces a right-footed shot from just outside the box that misses to the right of the goal.80:35
David Connolly is flagged offside by the assistant referee. Free kick taken by Matt Mills.79:47
Shot from just outside the box by Richie Wellens misses to the right of the goal.78:20
Nathan Delfouneso has an effort at goal from deep inside the area missing to the right of the goal.74:22 Substitution
Substitution Jermaine Beckford leaves the field to be replaced by Nathan Delfouneso.73:31 Booking
Booking David Nugent receives a yellow card.72:50
Free kick awarded for an unfair challenge on Jermaine Beckford by Daniel Fox. Lee Peltier takes the free kick.71:48
The ball is swung over by Frazer Richardson, save by Kasper Schmeichel.
Jermaine Beckford takes a shot. Save by Kelvin Davis.69:42
David Nugent takes a shot. Save made by Kelvin Davis.68:21
Daniel Fox produces a cross, Shot from close range by Frazer Richardson clears the bar.68:21 Booking
Booking Booking for Paul Konchesky for unsporting behaviour.68:15
Free kick awarded for an unfair challenge on Steve De Ridder by Paul Konchesky.67:01
Foul by Jermaine Beckford on Daniel Fox, free kick awarded. Daniel Fox restarts play with the free kick.64:04 Substitution
Substitution Frazer Richardson replaces Jos Hooiveld.61:38
Richie Wellens fouled by Steve De Ridder, the ref awards a free kick. Shot comes in from Paul Konchesky from the free kick. Richie Wellens crosses the ball, Headed effort on goal by David Nugent from just inside the box goes harmlessly over the target.61:02
Daniel Drinkwater produces a cross, Kelvin Davis makes a save.60:19
Effort from the edge of the box by Guly Do Prado goes wide of the right-hand upright.59:25
The ball is swung over by Neil Danns.58:48
Inswinging corner taken right-footed by Neil Danns, clearance made by Aaron Martin.58:42
The ball is sent over by David Nugent, blocked by Jack Cork.58:15
Free kick awarded for an unfair challenge on Jermaine Beckford by Morgan Schneiderlin. Paul Konchesky takes the direct free kick.57:30
Neil Danns has an effort at goal from just outside the penalty box which goes wide of the left-hand post.56:46
Free kick awarded for a foul by Morgan Schneiderlin on Neil Danns. Kasper Schmeichel takes the free kick.56:27
The assistant referee flags for offside against David Nugent. Kelvin Davis takes the free kick.55:21
Kasper Schmeichel restarts play with the free kick.55:21 Substitution
Substitution Steve De Ridder replaces Dean Hammond.55:21 Substitution
Substitution Iago Falque leaves the field to be replaced by Lee Holmes.55:21
Guly Do Prado is flagged offside by the assistant referee.53:37
Centre by Daniel Fox, Kasper Schmeichel fouled by Jos Hooiveld, the ref awards a free kick. Direct free kick taken by Kasper Schmeichel.52:57
Dan Harding fouled by Paul Konchesky, the ref awards a free kick. The ball is crossed by Daniel Fox, Dean Hammond takes a shot. Save by Kasper Schmeichel.52:31
A cross is delivered by Dan Harding, Sean St. Ledger manages to make a clearance.50:50
Shot from outside the area by David Nugent misses to the left of the target.49:18
The referee blows for offside against Guly Do Prado. Matt Mills takes the indirect free kick.48:55
David Connolly takes a shot. Kasper Schmeichel makes a comfortable save.47:49
Iago Falque fouled by David Nugent, the ref awards a free kick. Direct free kick taken by Dan Harding.47:09
A cross is delivered by Daniel Drinkwater, clearance by Jos Hooiveld.45:01
The second half kicks off.45:00 +2:31 Half time
Half Time The half-time whistle blows.45:00 +0:15
Iago Falque takes a shot. Lee Peltier gets a block in.44:04
Inswinging corner taken from the left by-line by Neil Danns, Headed effort from inside the area by Lee Peltier misses to the right of the target.41:08 Substitution
Substitution Daniel Drinkwater joins the action as a substitute, replacing Paul Gallagher.40:32
Shot from deep inside the area by Jack Cork clears the crossbar.38:04
The ball is crossed by Paul Gallagher, Kelvin Davis makes a save.37:35
Guly Do Prado concedes a free kick for a foul on Paul Gallagher. Direct free kick taken by Matt Mills.37:07
Shot from just outside the box by David Nugent goes over the bar.34:29
Richie Wellens produces a cross.32:24
Free kick awarded for a foul by Lloyd Dyer on Dan Harding. The ball is delivered by Dan Harding, Headed effort from inside the area by Dean Hammond misses to the right of the goal.32:00
Jermaine Beckford challenges Jos Hooiveld unfairly and gives away a free kick. Free kick taken by Kelvin Davis.27:14
Free kick awarded for an unfair challenge on Neil Danns by Iago Falque. Direct free kick taken by Richie Wellens.26:26
Free kick awarded for an unfair challenge on Daniel Fox by Jermaine Beckford. Free kick taken by Kelvin Davis.25:15
Assist by Sean St. Ledger.25:15 Goal scored
Goal! - Matt Mills - Southamp'n 0 - 2 Leicester Matt Mills grabs a headed goal from close in. Southampton 0-2 Leicester.25:14
A cross is delivered by Sean St. Ledger,24:45
Paul Gallagher takes the outswinging corner, Jos Hooiveld makes a clearance.24:35
Shot from 18 yards by Jermaine Beckford. Blocked by Jos Hooiveld.22:59
David Nugent produces a left-footed shot from the edge of the box and misses to the right of the goal.21:28
A cross is delivered by Iago Falque.20:20
Jermaine Beckford is ruled offside. Kelvin Davis restarts play with the free kick.19:24
Inswinging corner taken from the right by-line by Daniel Fox, free kick awarded for an unfair challenge on Kasper Schmeichel by Jos Hooiveld. Kasper Schmeichel takes the direct free kick.19:03
Daniel Fox produces a cross. Morgan Schneiderlin takes a shot. Matt Mills gets a block in.17:56
Richie Wellens challenges Iago Falque unfairly and gives away a free kick. Morgan Schneiderlin restarts play with the free kick.17:12
Daniel Fox produces a cross, save by Kasper Schmeichel.14:48
Matt Mills provided the assist for the goal.14:48 Goal scored
Goal! - David Nugent - Southamp'n 0 - 1 Leicester David Nugent finds the net with a goal from just outside the penalty box to the top right corner of the goal. Southampton 0-1 Leicester.11:34
David Connolly has an effort at goal from 20 yards. Save made by Kasper Schmeichel.10:44
Shot by Jermaine Beckford went wide left of the target.7:44
The ball is delivered by David Connolly, Kasper Schmeichel makes a comfortable save.5:51
Foul by Morgan Schneiderlin on Paul Gallagher, free kick awarded. Matt Mills takes the direct free kick.4:41
Corner taken by Paul Gallagher from the left by-line, Jos Hooiveld makes a clearance.3:42
The ball is crossed by Iago Falque. Shot from just outside the area by David Connolly misses to the left of the target.3:07
Lloyd Dyer sends in a cross.0:43
The ball is crossed by Paul Konchesky, Jermaine Beckford produces a left-footed shot from deep inside the penalty box which goes wide of the left-hand post.0:00
The referee gets the game started.
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