Watford had Chelsea largely where they wanted them for 80 minutes. The hosts led 1-0 through a fine Etienne Capoue strike and although they were sitting back a little too much, their organisation and application was ensuring they were dealing well with the relatively subdued attacking threat Chelsea were offering. But it was the visitors who were to secure the three points as the Hornets were dealt another harsh Premier League lesson.

The difference was to be two mistakes. Heurelho Gomes let a Eden Hazard shot squirm away from his body which substitute Michhy Batshuayi pounced on for the equaliser and with three minutes of normal time remaining, a poor pass from Adlene Guedioura was seized on by Cesc Fabregas and within seconds Diego Costa, who was fortunate to still be on the pitch, had netted the winner.

The 2-1 defeat was tough on the hosts, who at least looked like getting a point after taking the lead, and had shaded the exchanges before going in front in impressive fashion when Capoue fired home his second goal in as many games following a Guedioura cross.

Watford had previously edged a tight first half and had the better of what few chances were created, the best coming when the excellent Nordin Amrabat crossed low for Odion Igahlo to help the ball narrowly over the crossbar from close range.

Walter Mazzarri opted to keep faith with the same XI that started the season with a point in a 1-1 draw at Southampton, but with Ben Watson suspended following his sending off summer arrival Abdoulaye Doucoure was on a bench that also featured Tommie Hoban.

Antonio Conte made just the one change to the team that beat West Ham United 2-1 on Monday night with Pedro replacing Willian, while the Blues bench included former Hornets loanee Nathaniel Chalobah.

An already upbeat atmosphere was lifted when new signings Roberto Pereyra and Younes Kaboul were paraded on the pitch before kick-off, but the opening stages were a case of both sides feeling each other out in the breezy conditions.

Costa won a first corner for the visitors in the sixth minute but Hazard’s delivery from the right was competently dealt with by the Hornets. But within a minute Miguel Britos’ clipped ball over the top put Jose Holebas in behind the Chelsea defence on the left side of the penalty area and the Greek’s low drive was blocked by the legs of Thibaut Courtois.

The next opening came Chelsea’s way in the 11th minute when Hazard got away from Craig Cathcart on the right side of the 18-yard box and his dangerous ball bisected the six-yard area before a combination of Britos and Holebas prevented Costa from getting on the end of it at the back post.

Watford had more than held their own in the opening quarter-of-an-hour, although Oscar was to have a shooting opportunity from the edge of the area but dragged it harmlessly wide.

The match had been simmering nicely and in the 19th minute Jon Moss reached into his pocket for the first time to book Troy Deeney for illegally curtailing Hazard’s attempted break in the centre circle. At the same time though, the referee also showed a yellow card to Gary Cahill after he had left a boot in on Etienne Capoue moments earlier.

But in the 24th minute the Hornets went very close to taking the lead when Ighalo broke from his own half. He fed Amrabat to his right and the Moroccan advanced, doing very well to hold off Cesar Azpilicueta before delivering a fine low cross into the six-yard box where a sliding Ighalo got to the ball ahead of Cahill, but struck his effort into the ground and bouncing narrowly over Courtois’ crossbar.

Another promising situation arose for the hosts when Guedioura showed good feet to work some space in midfield to find Capoue, who in turn spread play out to Holebas on the left. He slipped on a pitch dampened by a brief downpour before regaining his feet and crossing to the near post where the ball was headed away from Ighalo and Guedioura’s eyes lit up as the ball broke for him, but he rushed his first-time half-volley and fired it high and wide of the target.

Watford were defending quite deep but were looking relatively untroubled until shortly before half time when Heurelho Gomes blocked an angled effort from Nemanja Matic, but the ball squirmed from his grasp and then proceeded to get in a mix up with Guedioura, who was trying to shepherd the ball back to his keeper and in the end just about got away with it.

Mazzarri received a talking to from the referee for protesting the award of a free-kick in injury time to the left of centre just outside the penalty area which ended with Hazard trying to catch Gomes out with a quickly taken low effort, but the Hornets keeper read his intentions and saved comfortably as a compelling opening period ended goalless.

The pattern of the game remained unchanged following the resumption but the first chance arrived in the 52nd minute when Oscar’s dangerous cross from the right was too far ahead of the stretching Costa, but Hazard met it beyond the far post with a first-time effort wide.

But three minutes later Watford were to take the lead in superb finish from what feels like a newly-found French scoring midfielder.

The Hornets’ first goal of the season at Vicarage Road originated from the right from where Guedioura hit a deep cross and the ball sat up invitingly for Capoue to strike a rapier-like half-volley beyond Courtois and inside his near post to make it two in two games and put the Hornets 1-0 to the good.

Costa was booked for dissent following the goal and he was fortunate to escape a second booking later in the half, having theatrically gone to ground looking for a penalty.

Chelsea sought an immediate response but much of their forward play had lacked conviction and that trend continued with Matic dragging a shot wide from the edge of the 18-yard box.

Watford had another promising situation in the 65th minute when they won a free-kick in a central position 25 yards out, but Holebas’ left-footed strike was unable to penetrate the wall.

The visitors were gradually lifting their game though, and Britos was to see yellow for bringing down Hazard and then, before the free-kick was taken, Holebas was also booked for dissent before the Hornets managed to see off that particular threat.

Conte made the first change, replacing Pedro with Victor Moses, but the game was being increasingly played in the Hornets’ half with Chelsea knocking at the door with increasing regularity and Watford looking increasingly content to try and sit on their lead.

Batshuayi came on for Oscar with 17 minutes of normal time to go as Conte switched to playing two up top but the Hornets were continuing to stick at the task diligently.

Conte played his final card with 12 minutes remaining, bringing on Fabregas for Matic much to the pleasure of a section of the visiting support. And within two minutes they were to shouting even louder when their side equalised.

There wasn’t too much apparent danger when the ball was worked to Hazard 25 yards out and he struck a right-footed shot. It was hit firm enough but Gomes would still have expected to keep hold of it, but the ball broke loose and Batshuayi was onto it in a flash to make it 1-1.

The Hornets then lost Capoue to injury after he was caught late by Costa, with Doucoure coming on in his place, but with three minutes to go most of Vicarage Road was plunged into silence and it was the hosts who really own had themselves to blame.

The Hornets were actually in quite an encouraging situation when Guedioura opted not to pass outside to Amrabat and look inside to Doucoure instead. But the attempted pass was seized upon by Fabregas and in an instant a ball upfield split Cathcart and Sebastian Prodl and Costa was away, closing in on Gomes before sliding the ball past him to make it 2-1.

Mazzarri threw on Matej Vydra and Juan Camilo Zuniga in an effort to get something from five minutes of injury time, but it was the Blues who nearly netted a third in injury time when Batshuayi thumped a left-footed shot off the crossbar with Gomes beaten.

Watford: Gomes; Cathcart, Prodl, Britos; Amrabat, Guedioura (Vydra 87), Behrami, Capoue (Doucoure 84), Holebas (Zuniga 90); Deeney, Ighalo. Not used: Pantilimon, Nyom, Anya, Hoban.

Chelsea: Courtois; Ivanovic, Cahill, Terry, Azpilicueta; Kante; Pedro (Moses 70), Oscar (Batshuayi), Matic (Fabregas 78), Hazard; Diego Costa. Not used: Begovic, Loftus-Cheek, Chalobah, Aina.

Bookings: Deeney for a foul on Hazard (19); Cahill for a foul on Capoue (19); Costa for dissent (50); Britos for a foul on Hazard (69); Holebas for dissent (70); Hazard for dissent (90); Behrami for a foul on Moses (90).

Attendance: 20,772 (2,119 away fans).

Referee: Jon Moss.