Motherwell tightened their grip on third position as they brushed aside the challenge of St Johnstone to move seven points clear of their hosts.
Omar Daley opened the scoring on the 16-minute mark when he tapped in Nicky Law's cross from the right.
The Fir Park team increased their advantage midway through the first half when Jamie Murphy headed Tom Hateley's centre past Peter Enckelman.
Murphy deflected Daley's 20-yard drive home to seal victory on 68 minutes.
The first chance came for the Lanarkshire side when Law was put through on goal by Michael Higdon, but he could only sweep a left-foot effort well wide from around eight yards.
St Johnstone responded immediately and a Carl Finnigan reverse pass found Murray Davidson in the penalty area, only for Darren Randolph to block the effort with his knees.
Steve Lomas' side kept up the pressure and Chris Millar floated a cross over from the right that was won in the air by Liam Craig. However, the ball was handled in a goalmouth scramble and the opportunity was lost.
Motherwell next made St Johnstone pay as they forged ahead through Daley. Law drilled a ball from the left across the six-yard box that neither Enckelman nor Callum Davidson could cut out and the winger converted from close range.
The home team tried to respond and a Craig cross from the left reached the head of Davidson, but the midfielder's header looped just wide.
Stuart McCall's men again showed a clinical edge to double their lead.
Daley was fouled by Davidson, but referee Alan Muir played advantage, Hateley swept in a cross from the right and Murphy's header beat Enckelman and nestled in the bottom left-hand corner of the net.
The Jamaican was in the mood and threatened again just before half-time.
He burst through the home defence and was brought down by the goalkeeper, but Muir ruled that the Finn had played the ball and gave a corner, with little complaints from the visitors.
St Johnstone were having plenty of possession in the early stages of the second half but failed to seriously test Randolph in the Motherwell goal.
However, that man Daley continued to be a danger and, on the hour mark, he danced into the penalty area and got a fierce shot away that Enckelman parried to safety.
He proved pivotal once again as Motherwell sealed victory with a third goal.
A short corner was relayed to the pacy forward 25 yards out and his shot deflected off Murphy and into the net.
The McDiarmid Park side launched a desperate final foray in the closing stages.
However, Motherwell coped comfortably with the best efforts of the home side and secured what could prove to be a crucial victory over their rivals.
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Live Text Commentary
Full Time The referee blows his whistle to end the game.90:00 +0:13
Outswinging corner taken by William Gibson, Effort on goal by Liam Craig from just inside the penalty area goes harmlessly over the target.89:57
Liam Craig has an effort at goal from just inside the box that misses to the right of the target.89:23
Steve Jennings takes a shot. Save by Peter Enckelman.88:43
Unfair challenge on Chris Humphrey by Chris Millar results in a free kick. Tom Hateley takes the direct free kick.88:10
Liam Craig takes a shot from just outside the penalty area clears the crossbar.87:36
Michael Higdon gives away a free kick for an unfair challenge on David McCracken. Peter Enckelman restarts play with the free kick.86:20
The ball is crossed by Liam Craig, Steve Jennings makes a clearance.81:46
The ball is delivered by William Gibson, Tom Hateley makes a clearance.80:18 Substitution
Substitution (Motherwell) makes a substitution, with Chris Humphrey coming on for Omar Daley.78:27
Liam Craig sends in a cross.77:34
Steve Jennings gives away a free kick for an unfair challenge on Chris Millar. Chris Millar takes the direct free kick.76:29 Substitution
Substitution Keith Lasley goes off and Stephen Hughes comes on.75:25
Marcus Haber is ruled offside. Darren Randolph takes the free kick.74:35
Corner taken left-footed by Liam Craig, clearance by Keith Lasley.74:24
The ball is swung over by William Gibson, clearance made by Tom Hateley.72:57
Shot by William Gibson from just outside the area goes over the net.71:48
Chris Millar produces a cross, save by Darren Randolph.70:50 Substitution
Substitution Carl Finnigan goes off and Sam Parkin comes on.69:42
Outswinging corner taken from the left by-line by Liam Craig, Shaun Hutchinson manages to make a clearance.
Assist on the goal came from Omar Daley.67:19 Goal scored
Goal! - Jamie Murphy - St J'stone 0 - 3 Motherwell Jamie Murphy grabs a goal from just inside the penalty area to the bottom left corner of the goal. St Johnstone 0-3 Motherwell.66:49
Inswinging corner taken right-footed by Tom Hateley,66:18
Jamie Murphy produces a cross, Steven Anderson manages to make a clearance.65:42
Murray Davidson produces a right-footed shot from outside the penalty box and misses wide left of the target.64:40
The ball is swung over by David MacKay, clearance by Tom Hateley.63:39 Substitution
Substitution (St Johnstone) makes a substitution, with William Gibson coming on for David Robertson.62:07
Murray Davidson takes a shot.61:39
Unfair challenge on Chris Millar by Michael Higdon results in a free kick. Liam Craig restarts play with the free kick.59:30
Omar Daley has an effort at goal from just inside the box that misses to the right of the target. Inswinging corner taken left-footed by Tom Hateley, Michael Higdon produces a header from inside the area that goes over the bar.56:46 Booking
Booking The referee shows Keith Lasley a yellow card for unsporting behaviour.56:38
Keith Lasley gives away a free kick for an unfair challenge on Steven Anderson. Steven Anderson takes the free kick.54:39
Foul by Steve Jennings on David MacKay, free kick awarded. Liam Craig takes the direct free kick, Shot from just outside the box by David MacKay goes over the target.54:02
Stevie Hammell challenges Chris Millar unfairly and gives away a free kick. Liam Craig takes the direct free kick.53:26
Stevie Hammell fouled by Murray Davidson, the ref awards a free kick. Stevie Hammell takes the direct free kick.51:21
Foul by Shaun Hutchinson on Marcus Haber, free kick awarded. Steven Anderson restarts play with the free kick.47:40
Stevie Hammell concedes a free kick for a foul on Murray Davidson. David MacKay takes the free kick.45:01
The match restarts for the second half.45:00 +1:35 Half time
Half Time The first half comes to an end.45:00 +1:23
The ball is sent over by Tom Hateley, Steven Anderson makes a clearance.45:00 +0:53
A cross is delivered by Carl Finnigan, clearance made by Stephen Craigan.43:30
Jamie Murphy fouled by Chris Millar, the ref awards a free kick. Direct effort from the free kick comes in from Tom Hateley, save by Peter Enckelman.42:50
Free kick awarded for a foul by Marcus Haber on Stephen Craigan. Stevie Hammell restarts play with the free kick.41:50
Inswinging corner taken right-footed by Tom Hateley, clearance by Liam Craig.36:33 Booking
Booking Booking for David Robertson for unsporting behaviour.36:25
Unfair challenge on Nicky Law by David Robertson results in a free kick. Darren Randolph takes the free kick.34:36
Carl Finnigan gives away a free kick for an unfair challenge on Stephen Craigan. Darren Randolph takes the direct free kick.33:02
Murray Davidson has a headed effort at goal from just inside the penalty area that misses to the right of the goal.30:41
Unfair challenge on Carl Finnigan by Shaun Hutchinson results in a free kick. Direct free kick taken by David Robertson. David MacKay takes a shot. Steve Jennings gets a block in.27:34
Assist by Tom Hateley.27:34 Goal scored
Goal! - Jamie Murphy - St J'stone 0 - 2 Motherwell Jamie Murphy finds the net with a headed goal from inside the penalty box. St Johnstone 0-2 Motherwell.27:34
The ball is delivered by Tom Hateley,25:17
Inswinging corner taken from the left by-line by Liam Craig. Marcus Haber concedes a free kick for a foul on Stephen Craigan. Darren Randolph takes the direct free kick. Michael Higdon gives away a free kick for an unfair challenge on David McCracken. David McCracken restarts play with the free kick.25:10
The ball is crossed by Marcus Haber, blocked by Stephen Craigan.24:45
Nicky Law sends in a cross, Steven Anderson makes a clearance.22:16
Omar Daley concedes a free kick for a foul on Murray Davidson. Callum Davidson takes the direct free kick.21:16
Nicky Law crosses the ball, blocked by David McCracken.18:48
Corner from the right by-line taken by Liam Craig, save made by Darren Randolph.18:16
Free kick awarded for a foul by Keith Lasley on David Robertson. Direct free kick taken by Steven Anderson.15:51
Assist on the goal came from Nicky Law.15:51 Goal scored
Goal! - Omar Daley - St J'stone 0 - 1 Motherwell Goal scored by Omar Daley from close in to the bottom right corner of the goal. St Johnstone 0-1 Motherwell.15:51
Nicky Law delivers the ball,14:00
Centre by Chris Millar. The referee gives a free kick against Carl Finnigan for handball. Darren Randolph takes the free kick. Michael Higdon is ruled offside. David Robertson takes the free kick.12:44
Unfair challenge on Chris Millar by Michael Higdon results in a free kick. Free kick taken by David MacKay.11:39
Michael Higdon is caught offside. Steven Anderson crosses the ball from the free kick right-footed from own half.9:34
Carl Finnigan gives away a free kick for an unfair challenge on Omar Daley. Free kick taken by Shaun Hutchinson.6:52
Shot by Murray Davidson. Save by Darren Randolph.3:48
A cross is delivered by Chris Millar, clearance by Steve Jennings.3:15
Omar Daley takes a shot. Peter Enckelman makes a save.2:02
Chris Millar crosses the ball, Stevie Hammell gets a block in.1:12
Jamie Murphy takes a shot.0:00
The ref blows the whistle to begin the match.
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