Peterborough moved clear of the relegation zone and struck a blow to their visitors' automatic promotion hopes with a 3-2 win against Watford.
Danny Swanson broke away to score on the half-hour mark before Dwight Gayle doubled Posh's lead after half-time.
Hornets defender Marco Cassetti saw red for hauling down Gayle and Lee Tomlin fired home the resulting free-kick.
Watford staged a late comeback with Mark Yeates and Fernando Forestieri both firing in from outside the box.
However it was not enough to rescue a point, and the result leaves them six points behind second-placed Hull with four games to play.
Peterborough meanwhile, pull one point clear of Barnsley in 22nd, while also extending their unbeaten run to nine matches.
In an open first half, Gayle shot narrowly wide for the hosts, while Forestieri and Nathaniel Chalobah saw chances go begging at the other end.
Gayle turned provider for the opening goal, sending Swanson free to place his shot past Manuel Almunia.
Posh doubled their lead on the hour, Gayle and Tomlin breaking free from the Watford back-line and exchanging passes before Gayle slotted home.
A packed away end suffered another blow moments later, as last-man Cassetti was judged to have bundled Gayle off the ball just outside the box.
Tomlin stepped up to blast home the free-kick into the top corner of Almunia's net.
As the match drew to a close, Yeates saw his deflected free-kick beat Robert Olejnik before Forestieri struck to ensure a nervy finish for the hosts.
Peterborough manager Darren Ferguson:
"For 70 minutes we were absolutely outstanding but we were all over the place for the last 20 and that is not good enough at this level.
"Staying in this division could come down to goal difference at the end of the season and those two Watford goals could be costly for us.
"We stopped doing the things that had put us in control but I still have to give the lads credit for another great result. I felt before today that three wins would keep us up and we've got the first of them.
"With four matches to go our destiny is in our hands. We've been on a great run but have to keep that pedal pressed to the floor and continue upping the ante."
Watford manager Gianfranco Zola:
"It was a bad day for us and getting automatic promotion will now be very tough, but we will keep on fighting as you never know what can happen in football. We battled on until the end and could even have got a draw if the game had lasted a little bit longer.
"We paid the price for making some stupid mistakes and also for a couple of decisions that the referee could have made in our favour.
"I thought we should have had two penalties which were not given, and it is not the first time this has happened to us. I see things on the pitch that make me believe we have not been treated well and I said that to the referee."
Full Time The final whistle goes and the game is over.
Effort on goal by Fernando Forestieri from just inside the penalty box goes harmlessly over the target.
Tommy Rowe challenges Matej Vydra unfairly and gives away a free kick. Free kick taken by Mark Yeates.
90:00 +4:11 Goal scored
Goal! - Fernando Forestieri - Peterboro 3 - 2 Watford Fernando Forestieri grabs a goal from just outside the area to the bottom left corner of the goal. Peterborough 3-2 Watford.
Mark Yeates produces a right-footed shot from just outside the box that goes wide left of the goal.
Matej Vydra decides to take a short corner.
Free kick awarded for an unfair challenge on Alex Pritchard by Matej Vydra. Direct effort from the free kick comes in from Grant McCann.
Matej Vydra takes a shot. Save by Robert Olejnik.
Florent Cuvelier is ruled offside. Lloyd Doyley takes the indirect free kick.
Shot from close range by Dwight Gayle misses to the right of the goal.
Inswinging corner taken by Mark Yeates, Shaun Brisley makes a clearance.
Troy Deeney provided the assist for the goal.
84:40 Goal scored
Goal! - Mark Yeates - Peterboro 3 - 1 Watford Mark Yeates hits the back of the net with a goal direct from the free kick from just outside the penalty area to the bottom left corner of the goal. Peterborough 3-1 Watford.
Shaun Brisley challenges Troy Deeney unfairly and gives away a free kick.
Almen Abdi produces a right-footed shot from the edge of the box and misses to the left of the target.
Ikechi Anya has an effort at goal from outside the penalty box missing to the wide right of the goal.
Corner taken by Almen Abdi played to the near post, clearance made by Grant McCann.
Outswinging corner taken by Almen Abdi from the right by-line played to the near post, clearance made by Shaun Brisley.
Tommy Rowe takes a shot. Save by Manuel Almunia. Effort from inside the area by Florent Cuvelier misses to the right of the target.
Corner from the right by-line taken by Grant McCann, free kick awarded for an unfair challenge on Almen Abdi by Tommy Rowe. Direct free kick taken by Manuel Almunia.
Indirect free kick taken by Robert Olejnik.
Substitution (Peterborough) makes a substitution, with Alex Pritchard coming on for Lee Tomlin.
Substitution Danny Swanson goes off and Florent Cuvelier comes on.
The referee blows for offside.
Danny Swanson takes a shot. Adam Thompson gets a block in.
Lee Tomlin delivers the ball.
Danny Swanson gives away a free kick for an unfair challenge on Mark Yeates. Direct free kick taken by Mark Yeates.
Grant McCann challenges Fernando Forestieri unfairly and gives away a free kick. Mark Yeates restarts play with the free kick.
Grant McCann produces a left-footed shot from long distance which goes wide right of the goal.
Substitution Adam Thompson replaces Jonathan Hogg.
Lee Tomlin gives away a free kick for an unfair challenge on Manuel Almunia. Free kick taken by Manuel Almunia.
Assist on the goal came from Dwight Gayle.
66:25 Goal scored
Goal! - Lee Tomlin - Peterboro 3 - 0 Watford Lee Tomlin hits the back of the net with a goal direct from the free kick from just outside the penalty box to the top left corner of the goal. Peterborough 3-0 Watford.
Dismissal Marco Cassetti receives a red card for professional foul.
Marco Cassetti gives away a free kick for an unfair challenge on Dwight Gayle.
Dwight Gayle fouled by Lloyd Doyley, the ref awards a free kick. Nathaniel Knight-Percival takes the direct free kick.
Substitution Mark Yeates joins the action as a substitute, replacing Nathaniel Chalobah.
Almen Abdi takes a shot. Save by Robert Olejnik.
Lee Tomlin provided the assist for the goal.
60:05 Goal scored
Goal! - Dwight Gayle - Peterboro 2 - 0 Watford Dwight Gayle finds the net with a goal from inside the box to the bottom right corner of the goal. Peterborough 2-0 Watford.
Lee Tomlin is penalised for a handball. Manuel Almunia restarts play with the free kick.
Almen Abdi takes a outswinging corner from the right by-line to the near post, Gabriel Zakuani makes a clearance.
Almen Abdi takes the outswinging corner, clearance by Gabriel Zakuani.
Lee Tomlin takes a shot. Manuel Almunia makes a save.
Pass corner from left by-line taken by Matej Vydra to short.
Tommy Rowe concedes a free kick for a foul on Fernando Forestieri. Free kick crossed right-footed by Almen Abdi from right wing, clearance by Shaun Brisley.
Marco Cassetti takes the direct free kick.
Booking The referee books Danny Swanson for unsporting behaviour.
Foul by Danny Swanson on Matej Vydra, free kick awarded.
Corner taken by Lee Tomlin from the left by-line, Manuel Almunia makes a save.
Unfair challenge on Nathaniel Chalobah by Lee Tomlin results in a free kick. Nathaniel Chalobah takes the direct free kick.
The ball is sent over by Jonathan Hogg, comfortable save by Robert Olejnik.
Craig Alcock gives away a free kick for an unfair challenge on Ikechi Anya. The free kick is delivered right-footed by Fernando Forestieri from left wing, Matej Vydra manages to make a clearance.
Lee Tomlin takes the inswinging corner, Dwight Gayle challenges Manuel Almunia unfairly and gives away a free kick. Free kick taken by Manuel Almunia.
The second half begins.
Substitution (Watford) makes a substitution, with Matej Vydra coming on for Joel Ekstrand.
45:00 +4:42 Half time
Half Time The half-time whistle blows.
Corner taken right-footed by Lee Tomlin, Danny Swanson gives away a free kick for an unfair challenge on Nathaniel Chalobah. Manuel Almunia restarts play with the free kick.
Joel Ekstrand gives away a free kick for an unfair challenge on Dwight Gayle. Free kick crossed left-footed by Grant McCann from right channel, save by Manuel Almunia.
Clearance by Almen Abdi.
45:00 +1:18 Substitution
Substitution Mark Little goes off and Shaun Brisley comes on.
Corner taken by Lee Tomlin played to the near post,
Foul by Lee Tomlin on Ikechi Anya, free kick awarded. Direct free kick taken by Manuel Almunia.
Troy Deeney takes a shot. Nathaniel Knight-Percival gets a block in.
Fernando Forestieri crosses the ball.
Inswinging corner taken by Almen Abdi from the left by-line.
Lloyd Doyley takes the direct free kick.
Booking Lee Tomlin is shown a yellow card.
Foul by Lee Tomlin on Nathaniel Chalobah, free kick awarded.
Nathaniel Chalobah concedes a free kick for a foul on Kane Ferdinand. Robert Olejnik restarts play with the free kick.
Booking The referee shows Troy Deeney a yellow card for dissent.
Joel Ekstrand fouled by Dwight Gayle, the ref awards a free kick. Manuel Almunia takes the free kick.
Fernando Forestieri fouled by Craig Alcock, the ref awards a free kick. Strike on goal comes in from Almen Abdi from the free kick.
Effort from the edge of the area by Daniel Pudil goes wide of the left-hand post.
Assist by Dwight Gayle.
28:27 Goal scored
Goal! - Danny Swanson - Peterboro 1 - 0 Watford Danny Swanson scores a goal from inside the box to the bottom left corner of the goal. Peterborough 1-0 Watford.
Troy Deeney produces a right-footed shot from the edge of the box and misses to the left of the goal.
Jonathan Hogg takes a shot. Save by Robert Olejnik.
Jonathan Hogg fouled by Grant McCann, the ref awards a free kick. Jonathan Hogg takes the free kick.
Dwight Gayle fouled by Daniel Pudil, the ref awards a free kick. Direct free kick taken by Grant McCann.
Nathaniel Chalobah has an effort at goal from outside the penalty box which goes wide right of the target.
Fernando Forestieri takes a shot. Craig Alcock gets a block in.
Corner taken by Almen Abdi from the right by-line, Gabriel Zakuani manages to make a clearance.
Effort from the edge of the area by Daniel Pudil goes wide of the left-hand post.
Unfair challenge on Danny Swanson by Nathaniel Chalobah results in a free kick. Grant McCann takes the direct free kick.
Lee Tomlin takes a shot. Save by Manuel Almunia.
Lee Tomlin crosses the ball in from the free kick, Troy Deeney manages to make a clearance.
Booking The referee shows Joel Ekstrand a yellow card for unsporting behaviour.
Free kick awarded for a foul by Joel Ekstrand on Dwight Gayle.
Daniel Pudil produces a cross, Tommy Rowe manages to make a clearance.
Almen Abdi challenges Nathaniel Knight-Percival unfairly and gives away a free kick. Grant McCann restarts play with the free kick.
Effort from the edge of the area by Dwight Gayle goes wide of the right-hand upright.
Troy Deeney takes a shot. Save made by Robert Olejnik.
Tommy Rowe produces a cross, clearance made by Joel Ekstrand.
Mark Little concedes a free kick for a foul on Almen Abdi. Direct free kick taken by Daniel Pudil.
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