Chelsea brushed off their midweek setback to return to winning ways with a routine 3-0 victory over Watford at Stamford Bridge
Frank Lampard had called for a response from his players following his side's , and after  temporarily moved above them into the top four with a comprehensive victory over Bournemouth on Saturday, Chelsea had to win
Olivier Giroud was one of four changes to the side by Lampard, and he marked his return with the opener, finding the bottom corner with a left-foot shot (28) to break the deadlock
 The Blues doubled their lead two minutes before the break as Willian converted from the spot following a foul by Etienne Capoue on Christian Pulisic
At times, Chelsea controlled the second period like a training game, but Ross Barkley added extra gloss to the scoreline as he met Cesar Azpilicueta's cross to slam home a smart finish at the near post (90+2)
The result means Chelsea leapfrog United by two points back into fourth spot while Watford remain precariously placed, one position and a solitary point above the relegation zone ahead of 18th-placed Aston Villa, who visit Liverpool on Sunday, live on 
The Blues almost seized upon the game's first gilt-edged chance after 19 minutes, with Watford regimented but struggling for creativity, as Giroud was found by Pulisic inside the area but his low shot was saved by the feet of Ben Foster
But the Frenchman handed the hosts a 1-0 lead with his fourth Premier League goal of the season in the 28th minute, angling home after a smart ball from Ross Barkley
Watford haven't won away at Chelsea in any competition since May 1986, and they were facing down the barrel of another defeat two minutes before half-time when Pulisic was taken down in the box by Capoue
Willian was allowed to bury another spot-kick, just as he had in Wednesday's loss, meaning the Brazilian has now scored more goals (9) and had more goal involvements (14 - 9 goals, 5 assists) in the Premier League this season than any other campaign in the competition
"Capoue decided to make a really bad, really rash decision, and he's cost his team," Jamie Redknapp told  at the interval
Despite the need for urgency from the Hornets, Chelsea emerged the far more proactive side following the restart, with Lampard determined to avoid a repeat of the disappointment at the London Stadium in midweek
His side almost went further in front as Giroud was found in space on the hour-mark by the lively Willian but this time his low shot was smothered from close range by the overworked Foster
"It's attack against defence, this
 It's so simple for Chelsea," Alan Smith said on co-commentary - and Foster had to be on his toes as he sprawled across goal to keep out another Willian shot from Barkley's lay-off
Pearson's side had offered a non-existent threat, but Kepa Arrizabalaga had to be alert to a speculative shot from distance from substitute Adam Masina before Craig Dawson headed over Will Hughes' free-kick with 15 minutes remaining
The Hornets flickered into life as the returning Nathaniel Chalobah stole the ball off Billy Gilmour to release Danny Welbeck, but the striker's shot was tame and easily saved by Kepa to preserve a rare Chelsea clean sheet
Welbeck certainly added to Watford's attack since his introduction, and he so nearly provided his side with a late consolation and a potential nervy finish for the hosts as Ruben Loftus-Cheek produced a last-ditch tackle to prevent Hughes from tapping home his cut-back
But Chelsea had the final word as Barkley scored his first Premier League goal in 20 months in the second minute of stoppage time, blasting home Azpilicueta's cross at the near post
Chelsea boss : "We played some nice stuff and it can be difficult to play against the low block
 They came to defend so the way we broke it down was good
 We could've been a bit more incisive with our passing in the second half but I'm delighted with the clean sheet
 It was a comfortable evening for us
"Pre-West Ham, we could've gone third but we let ourselves down
 We slipped to fifth before today, and responded
 We need to get used to that sort of pressure, as it's going to be tough all the way through
"Watford boss : "I thought we played with discipline and I said to the players that's hard when you've got players who would normally contribute in a different way who are having to work particularly hard for the team to keep our shape and try to make it difficult for our opponents
"We'd like to have spent more time on the ball but we knew we'd see a response from them since their last game
 The subs had impact and we showed the qualities that were missing last week
"Time is not on our side in terms of games left so we have to be brave, and I thought we were tonight
"So often Lampard has put his trust in Mount and rightly so
 His passing accuracy of 88
9 per cent kept Chelsea in control, and he was only denied a goal his performance merited with two shots blocked
Alan Smith told : "There were a couple of stand-out performers, but Mount has become such an integral part of this Chelsea starting XI
"Lampard thinks a lot of him and he's shown once again his qualities tonight
"Mount told : "I'm quite surprised I got man of the match, to be fair! I was just trying to keep the ball and keep it ticking over
 Ross got a goal and an assist
"But it was a brilliant performance
 We spoke before the game that we needed to have a reaction and show what we can do
 It was a must-win game and we did that
"We took a loss against West Ham but that's how our season has gone
 We have bounced back from a lot of defeats and we showed again tonight that we can win when the pressure's on
 We just need to keep going now and get as many points as we can
"Christian Pulisic told : "I feel confident in my game right now and I'm happy to be on the field to help my team
 I'm just going to continue and keep my confidence high
Asked about the comparisons being made between himself and Eden Hazard, Pulisic added: "He was an incredible player for Chelsea and is a world class player so I'm not going to try to compare myself to him
 I'm just going to try to be my own player and hopefully the fans like that guy
"There's a little bit of extra energy because of the loss to West Ham
 We wanted to prove a point, and I think we did that
"Chelsea travel to face Crystal Palace at Selhurst Park on Tuesday, live on  (kick-off: 6pm)
Watford host Norwich at Vicarage Road at the same time on 
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