Match ends, Chelsea 2, Watford 2.
Chelsea 2-2 Watford
Diego Costa scored twice as Guus Hiddink's second spell as Chelsea boss started with a draw against Watford.
It could have been more for Hiddink, in charge after Jose Mourinho's sacking, had Oscar not missed a late penalty.
Spaniard Costa hooked in the opener for the Blues before Nemanja Matic's handball allowed Troy Deeney to level from the penalty spot.
Odion Ighalo's deflected shot gave the visitors the lead, only for Costa to fire in and earn Chelsea a point.
The Blues have won just one of their last five Premier League games and are 15th in the table, just two points above the relegation zone.
Watford's run of four successive victories came to an end, but they remain seventh.
Costa full of beans
Hiddink, placed in interim charge at Stamford Bridge this week almost seven years after his first stint as manager, should have been celebrating a win upon his return to the champions.
But after Valon Behrami cut down Eden Hazard in the penalty area, Brazilian Oscar slipped on his run up to his 80th-minute penalty and hit the ball against his standing leg, slicing it clear of the crossbar.
But while Chelsea were not as fluid as they were in last week's 3-1 win over Sunderland, overseen by caretaker boss Steve Holland, they will have been buoyed by the return to form of Costa.
With just three Premier League goals this season before the game, he showed the predatory instincts that saw him score 21 times last term - but a late booking means he will be suspended for the trip to Manchester United on Monday.
The 27-year-old opened the scoring by turning to half-volley in from six yards after John Terry knocked down Willian's corner and then timed his run perfectly to take in Willian's superb throughball and angle his shot past Heurelho Gomes for the equaliser.
Hiddink quietening Chelsea complainers?
Costa was one of three players, along with Cesc Fabregas and Oscar, who were berated last week by some Chelsea fans who were convinced the squad had cost Mourinho his job after losing nine of this season's first 16 league games.
But there was an air of positivity around Stamford Bridge, as Hiddink, who led the Blues to victory in the FA Cup final in 2009, was warmly greeted by home supporters.
The Dutchman told his players to look at themselves in the mirror this week, but barely changed the starting line-up, only bringing Gary Cahill in for Kurt Zouma in central defence.
But he seemed to give his full-backs - in particular Branislav Ivanovic - the licence to push forward and add width to his side, as he looks to pull Chelsea away from the drop zone and towards the top four before the end of the season.
How do Watford keep doing it?
Chelsea might have thought they were in for an easy afternoon after dominating possession for the first 15 minutes.
But Watford have won eight times this season after their promotion from the Championship, including last week's 3-0 dismantling of Liverpool, and recovered well to pose a constant threat to the home side.
A lot of their success is down to the forward partnership of Ighalo and Deeney, who held up the ball tremendously and both saw late efforts blocked, as well as a defence that had kept three clean sheets in its last three games.
Their leveller to make it 1-1 was a gift from Chelsea, as Matic got in a mess and handled Ben Watson's corner, allowing Deeney to stroke in his spot-kick for his sixth of the campaign.
And Cahill did not cover himself in glory as he backed off Ighalo, who strode into the area and hit a shot that deflected off the England defender and looped past Thibaut Courtois to give the Nigerian his 29th goal of 2015.
Man of the match - Willian
What they said
Chelsea interim manager Guus Hiddink: "At the end it is a fair result. You have to have respect for Watford because they have been on a winning streak and have very decent strikers.
"But in the end I think we could have made a little bit more, we had some chances and it was a pity Oscar slipped for the penalty.
"Diego Costa when he is focused on what he is good at he has his profit from his play.
"He will not be there [against Manchester United on Monday] which means we have to think a bit. [Eden] Hazard came back in the last week and had two training sessions and we hope he can be fully fit."
Watford manager Quique Flores: "I think we had the possibility to win but Chelsea played really well.
"They pushed us a lot and were probably closer to the win than us. We defended well, we fought a lot in the 90 minutes, and for us this is a very important point.
On whether Diego Costa was offside when scoring: "I don't know, it is very quick, probably if you say it is offside maybe it is offside, but anyway I think the result is fair.
"I think the team has enough confidence for the future, it's amazing for the story of Watford."
The stats you need to know
- Chelsea are unbeaten in the Premier League on Boxing Day since 2003, winning six and drawing five matches since then.
- Watford have won just two of their last 14 league matches played on Boxing Day (won two, drew five, lost seven).
- The Hornets have already won more points in 2015-16 than in any of their previous two Premier League campaigns (29).
- Diego Costa scored his first Premier League brace since 17 January versus Swansea City and it was only the second time that he scored more than once in a single Premier League game at Stamford Bridge.
- Willian - who assisted Costa's second goal - has had a hand in 10 goals in all competitions for Chelsea this season (seven goals, three assists).
- Odion Ighalo is the first Watford player to score in five successive top-flight games.
- Troy Deeney has been directly involved in six goals in his last seven Premier League appearances (five goals, one assist).
- Deeney's strike was Watford's first goal at Stamford Bridge since Allan Smart in February 2000 - they had failed to score in their last four competitive trips there.
Chelsea go to Manchester United on Monday, without the suspended Diego Costa, while Watford host Tottenham.
- 4FàbregasSubstituted forMikelat 45'minutes
- 17PedroSubstituted forE Hazardat 74'minutes
- 19Diego CostaBooked at 88mins
- 7Santos do Nascimento
- 10E Hazard
- 15CathcartBooked at 48mins
- 3BritosBooked at 44mins
- 25HolebasBooked at 81mins
- 22AbdiSubstituted forBehramiat 69'minutesBooked at 83mins
- 7JuradoSubstituted forAnyaat 73'minutes
- 9DeeneySubstituted forGuédiouraat 90+3'minutes
- Andre Marriner
- Shots on Target
Second Half ends, Chelsea 2, Watford 2.
Attempt missed. John Obi Mikel (Chelsea) right footed shot from outside the box is close, but misses to the right. Assisted by Willian.
Substitution, Watford. Adlène Guédioura replaces Troy Deeney.
Attempt blocked. Nemanja Matic (Chelsea) left footed shot from the right side of the box is blocked. Assisted by Branislav Ivanovic.
Gary Cahill (Chelsea) wins a free kick on the right wing.
Foul by Odion Ighalo (Watford).
Diego Costa (Chelsea) is shown the yellow card for a bad foul.
Foul by Diego Costa (Chelsea).
Craig Cathcart (Watford) wins a free kick in the defensive half.
Attempt blocked. Troy Deeney (Watford) right footed shot from the centre of the box is blocked.
Attempt blocked. Odion Ighalo (Watford) right footed shot from the left side of the box is blocked. Assisted by Troy Deeney.
Offside, Watford. Miguel Britos tries a through ball, but Ikechi Anya is caught offside.
Valon Behrami (Watford) is shown the yellow card for a bad foul.
César Azpilicueta (Chelsea) wins a free kick in the defensive half.
Foul by Valon Behrami (Watford).
José Holebas (Watford) is shown the yellow card for a bad foul.
Branislav Ivanovic (Chelsea) wins a free kick in the defensive half.
Foul by José Holebas (Watford).
Penalty missed! Bad penalty by Oscar (Chelsea) right footed shot is too high. Oscar should be disappointed.
Penalty Chelsea. Eden Hazard draws a foul in the penalty area.
Penalty conceded by Valon Behrami (Watford) after a foul in the penalty area.
Foul by Diego Costa (Chelsea).
Craig Cathcart (Watford) wins a free kick in the defensive half.
Attempt missed. Willian (Chelsea) right footed shot from outside the box is too high from a direct free kick.
Willian (Chelsea) wins a free kick in the attacking half.
Foul by Ben Watson (Watford).
Substitution, Chelsea. Eden Hazard replaces Pedro because of an injury.
Substitution, Watford. Ikechi Anya replaces Jurado.
Substitution, Watford. Valon Behrami replaces Almen Abdi.
Attempt missed. Diego Costa (Chelsea) right footed shot from the centre of the box is close, but misses to the left. Assisted by Oscar.
Pedro (Chelsea) wins a free kick in the defensive half.
Foul by Almen Abdi (Watford).
Goal! Chelsea 2, Watford 2. Diego Costa (Chelsea) right footed shot from the right side of the box to the bottom left corner. Assisted by Willian with a through ball.
Attempt blocked. Pedro (Chelsea) right footed shot from the centre of the box is blocked. Assisted by Oscar.
Attempt blocked. Nemanja Matic (Chelsea) left footed shot from outside the box is blocked. Assisted by Pedro.
Goal! Chelsea 1, Watford 2. Odion Ighalo (Watford) left footed shot from the left side of the box to the bottom left corner. Assisted by Jurado.
Attempt blocked. Etienne Capoue (Watford) right footed shot from the centre of the box is blocked.
Attempt saved. Etienne Capoue (Watford) right footed shot from outside the box is saved in the top centre of the goal.
Foul by John Obi Mikel (Chelsea).