Maurizio Sarri’s side were booed off after a sloppy first half, but two goals in three minutes from Loftus-Cheek and Luiz lifted the mood at Stamford Bridge.
Gonzalo Higuain added the third and Chelsea are now one point clear of fourth placed Tottenham after their first win in four games in all competitions.
If the Blues win their last league game of the season at Leicester next Sunday they will be certain to qualify for next season’s Champions League via a top-four finish.
Before heading to Leicester, Chelsea host Eintracht Frankfurt in the Europa League semi-finals on Thursday, with the tie poised at 1-1 after the first leg.
Finishing in the top four and winning the Europa League would make Sarri’s troubled first season a relative success.
But even now Sarri, who has struggled to win over his squad, can’t escape murmurs of dissent.
The former Napoli boss awoke to more unrest on Sunday after out-of-favour Blues defender Gary Cahill blasted Sarri.
Cahill has made just eight appearances this season and claims he has been shown a lack of respect by Sarri.
“I see some of the situations with players who won the title with Chelsea, not just myself, and it just hasn’t been right,” the long-serving Cahill told the Sunday Telegraph.
“It makes it very hard for me to have respect for someone who has not respected what some of us have won with the club.”
Cahill was given a standing ovation by Chelsea fans when Sarri sent him on in the final minutes for what could be his farewell appearance.
But Cahill’s outburst might have been on his team-mates’ minds during a lethargic, distracted first half display.
Watford’s Gerard Deulofeu went close early on with a fierce shot that flashed just wide.
– Hazard sparkles –
Chelsea were also indebted to a stunning save from Kepa Arrizabalaga, who recently admitted the painful lessons of his League Cup final mutiny — when he refused to be substituted against Manchester City — have made him a better person and player.
When Jose Holebas whipped in a cross, Kepa showed why Sarri only dropped him for one match following that Wembley rebellion as he leapt high to his right to brilliantly claw away Troy Deeney’s header from a Jose Holebas cross.
Adding to a concerning start for Chelsea, they lost France midfielder N’Golo Kante to injury after 10 minutes.
Loftus-Cheek, who started on the bench despite an impressive display in Frankfurt, came on for Kante, but Chelsea were still off the pace.
Deulofeu scuffed wide from a good position and by the time Holebas rifled just over from long-range, Sarri cut an agitated figure as he gesticulated angrily on the touchline.
Urging his players to “pass, pass, pass”, Sarri’s promptings almost brought a reward when Pedro went close with a 20-yard blast after a neat link-up with Gonzalo Higuain. It wasn’t enough to prevent half-time jeers.
But Eden Hazard was beginning to warm to his task and the Belgian, without whom Chelsea would be completely toothless, helped Sarri’s men silence the doubters in the 48th minute.
When Hazard took a short corner, he collected Pedro’s return pass and flicked a cross towards the far post, where Loftus-Cheek rose above Nathaniel Chalobah to head home from close-range.
Playing with more verve and belief now, Chelsea struck again from another corner three minutes later as Hazard’s delivery was met by Luiz with a thumping header past Foster.
Higuain put the result beyond doubt when he scored just the fifth goal of his loan spell from Juventus in the 75th minute.
Running onto Pedro’s pass, the Argentine striker clipped a delicate finish over Foster from a tight angle to cap Chelsea’s second half resurgence. (AFP)