By Owen PhillipsBBC Sport at the King Power Stadium
David Nugent's first goal in 17 games gave Leicester a slender and deserved lead over Watford after an open Championship semi-final first leg.
The Foxes dominated a gripping first half with a pacy and powerful display but missed a couple of fine chances.
Watford improved after the break and Matej Vydra and Alex Geijo both wasted glorious opportunities.
But Nugent headed in Anthony Knockaert's late free-kick to secure the win ahead of Sunday's second leg.
It was the striker's 15th goal of the season and, although it is his first since January, it could prove to be well worth the wait for a side whose play-off dream seemed to be over less than a week ago.
The Foxes were second in the table in February but a dismal end-of-season run saw them win just once in their final 12 games before last Saturday.
And once again the tremendous pace, direct running and trickery of Lloyd Dyer and Saturday's match-winner Knockaert was the standout feature of their attacking play.
Watford, the Football League's second-highest top scorers this season with 85 goals, were rattled, uncharacteristically sloppy, and barely got out of their half in the opening 15 minutes.
Nugent tested fit-again Hornets goalkeeper Manuel Almunia with a cheeky back-heel and had a decent strike blocked, and Ritchie De Laet headed straight at the former Arsenal man from point-blank range.
Jason Robertsspeaking on BBC Radio 5 live
Leicester have the advantage and rightly so. They were the better team on the day. Watford will be disappointed with what they created. But the tie is far from over and both teams have everything to play for in the return leg on Sunday
But having weathered the storm in blustery, rainy conditions at a heaving King Power Stadium they nearly went ahead.
A terrible defensive slip-up by
Manchester United trialist Jeffrey Schlupp
allowed Ikechi Anya to run through and Kasper Schmeichel had to be alert to block his strike and an even better follow-up effort from Almen Abdi.
Marco Cassetti also shot over from distance but Leicester remained the dominant side and responded again.
Nugent should have scored but side-footed wide from 12 yards after more great work by the jet-heeled Dyer and Knockaert went close after a lightning break and some smart footwork on the right flank.
The chances slowed up after the interval and the quality and excitement also dropped off. But the frantic pace remained.
Watford began to show the measure of control they had previously lacked and looked more comfortable in defence against Leicester's pace.
And they had two glorious chances to go ahead.
Far from over. . .
Watford, who finished third in the Championship table, may be trailing but they will be heartened by the fact that in each of the last two seasons the team finishing third has won promotion via the play-offs - West Ham and Swansea
Football League player of the year Vydra
should have scored but completely fluffed his kick when through one-on-one and Geijo headed over from six yards at the back post when he seemed to completely mistime his leap.
The Foxes made Watford pay when Knockaert swung over a teasing cross and Nugent rose to head in from close range and send the home fans into raptures and earn a vital lead prior to Sunday's second leg at Vicarage Road.
Leicester City manager Nigel Pearson:
"It's half-time, it was a tight game with two good sides. We were able to take a chance towards the end when it looked as though it was going to end 0-0 and it's all to play for.
"We've got to be positive and try and win the next game as well.
"The play-offs are always a bit difficult to negotiate in terms of anything can happen and both sides will feel they can win."
Watford manager Gianfranco Zola:
"I didn't expect them to score, I didn't see that coming at any time because it looked like we were in control of it.
"We had a few chances when we should have scored.
"But it's only half-time. We are looking forward to playing on Sunday.
"We have to win the game - that is what we want. It is going to be tough but we have a lot of confidence too."
Full Time The referee blows for the end of the match.
Harry Kane challenges Joel Ekstrand unfairly and gives away a free kick. Manuel Almunia takes the free kick.
Free kick taken by Michael Keane.
90:00 +3:21 Substitution
Substitution Danny Drinkwater is brought on as a substitute for Anthony Knockaert.
90:00 +3:21 Booking
Booking The referee shows Fitz Hall a yellow card.
Fitz Hall gives away a free kick for an unfair challenge on Andy King.
90:00 +1:52 Substitution
Substitution Fernando Forestieri replaces Matej Vydra.
Ikechi Anya has an effort at goal from outside the penalty box missing to the wide left of the goal.
Lloyd Dyer takes a shot. Marco Cassetti manages to make a clearance.
Free kick awarded for an unfair challenge on Harry Kane by Fitz Hall. Free kick taken by Anthony Knockaert.
Substitution Fitz Hall on for Lloyd Doyley.
Anthony Knockaert takes a shot. Manuel Almunia makes a comfortable save.
Assist by Anthony Knockaert.
81:10 Goal scored
Goal! - David Nugent - Leicester 1 - 0 Watford David Nugent finds the back of the net with a headed goal from inside the area. Leicester 1-0 Watford.
Free kick awarded for an unfair challenge on Harry Kane by Joel Ekstrand. Anthony Knockaert crosses the ball,
Inswinging corner taken right-footed by Almen Abdi from the left by-line.
Close range header by Alexandre Geijo goes over the crossbar.
A cross is delivered by Ritchie De Laet.
Jeff Schlupp gives away a free kick for an unfair challenge on Alexandre Geijo. Nathaniel Chalobah takes the direct free kick.
Free kick taken by Kasper Schmeichel.
Substitution Daniel Pudil goes off and Matthew Briggs comes on.
Booking Daniel Pudil is shown a yellow card.
Foul by Daniel Pudil on Ritchie De Laet, free kick awarded.
Matej Vydra has an effort at goal from 18 yards. Kasper Schmeichel makes a fantastic save. Anthony Knockaert is caught offside. Manuel Almunia restarts play with the free kick.
Matej Vydra takes the chance to get an effort at goal. Michael Keane gets a block in.
Foul by Almen Abdi on David Nugent, free kick awarded. Kasper Schmeichel restarts play with the free kick.
Anthony Knockaert gives away a free kick for an unfair challenge on Jonathan Hogg. Lloyd Doyley takes the free kick.
Substitution Harry Kane replaces Chris Wood.
Jonathan Hogg takes a shot. Kasper Schmeichel makes a comfortable save. Matej Vydra takes a shot. Kasper Schmeichel makes a comfortable save.
Almen Abdi produces a strike on goal direct from the free kick.
Booking Michael Keane goes into the referee's book for unsporting behaviour.
Free kick awarded for an unfair challenge on Alexandre Geijo by Michael Keane.
Unfair challenge on Anthony Knockaert by Marco Cassetti results in a free kick. Free kick taken by Kasper Schmeichel.
Shot from 20 yards by Matty James. Blocked by Joel Ekstrand. Outswinging corner taken left-footed by Anthony Knockaert played to the near post.
Jeff Schlupp has an effort from just inside the box that misses to the left of the goal.
Free kick awarded for a foul by Chris Wood on Daniel Pudil. Manuel Almunia restarts play with the free kick.
The second half begins.
Booking Anthony Knockaert goes into the book.
45:00 +2:17 Half time
Half Time The players leave the pitch at half time.
The referee blows for offside against Alexandre Geijo. Kasper Schmeichel takes the free kick.
Daniel Pudil has an effort at goal from 20 yards. Blocked by Ritchie De Laet. Almen Abdi takes the outswinging corner, Header on goal by Joel Ekstrand from inside the box goes harmlessly over the target.
Michael Keane produces a volleyed right-footed shot from deep inside the penalty box which goes wide of the left-hand upright.
Anthony Knockaert takes a shot. Save by Manuel Almunia. Anthony Knockaert takes the inswinging corner, Joel Ekstrand makes a clearance.
Direct strike on goal from the free kick comes in from Almen Abdi. Corner taken right-footed by Almen Abdi from the right by-line, clearance made by David Nugent.
Booking Wes Morgan receives a caution for unsporting behaviour.
Wes Morgan gives away a free kick for an unfair challenge on Matej Vydra.
Matty James gives away a free kick for an unfair challenge on Nathaniel Chalobah. Free kick taken by Marco Cassetti.
Nathaniel Chalobah takes a shot. Kasper Schmeichel makes a comfortable save.
Jeff Schlupp fouled by Almen Abdi, the ref awards a free kick. Anthony Knockaert delivers the ball from the free kick left-footed from left wing, Manuel Almunia makes a comfortable save.
Almen Abdi restarts play with the free kick. Ikechi Anya takes a shot. Jeff Schlupp gets a block in. Outswinging corner taken by Almen Abdi from the right by-line, Michael Keane makes a clearance.
Booking Jeff Schlupp is shown a yellow card.
Free kick awarded for a foul by Jeff Schlupp on Ikechi Anya.
David Nugent produces a right-footed shot from deep inside the penalty area which goes wide of the left-hand post. Handball by Nathaniel Chalobah. Michael Keane takes the free kick.
Daniel Pudil has an effort at goal from just inside the box that misses to the left of the goal.
Free kick awarded for an unfair challenge on Michael Keane by Matej Vydra. Direct free kick taken by Michael Keane.
Marco Cassetti takes a long range shot clearing the bar.
Ikechi Anya has an effort at goal. Kasper Schmeichel makes a save. Almen Abdi takes a shot. Save by Kasper Schmeichel. Matej Vydra takes a shot. Michael Keane gets a block in. Almen Abdi decides to take a short corner.
Matty James takes a shot. Ikechi Anya gets a block in. Matty James decides to take a short corner. Matty James takes the inswinging corner, Ritchie De Laet takes a shot. Save by Manuel Almunia.
Corner from the right by-line taken by Anthony Knockaert, Jonathan Hogg manages to make a clearance. David Nugent takes a shot. Blocked by Joel Ekstrand.
Free kick awarded for a foul by Lloyd Doyley on Chris Wood. Free kick crossed left-footed by Anthony Knockaert, comfortable save by Manuel Almunia.
Free kick crossed by Matty James.
Booking Ikechi Anya receives a caution.
Ikechi Anya concedes a free kick for a foul on Lloyd Dyer.
Lloyd Dyer sends in a cross.
David Nugent takes a shot. Save by Manuel Almunia.
Alexandre Geijo gives away a free kick for an unfair challenge on Michael Keane. Kasper Schmeichel takes the free kick.
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