It was a comfortable evening’s work at Stamford Bridge, with the result never in doubt from the moment Giroud cutely put us ahead shortly before the half-hour with his fifth goal of the season, and fourth in seven league games.

With the interval approaching, Willian doubled our lead from the spot after the lively Christian Pulisic was scythed down. The Brazilian is the first Chelsea player to convert from 12 yards in three consecutive Premier League matches.

In the second half Giroud, Pulisic and Willian might all have added to our tally before Barkley did in stoppage time, collecting Cesar Azpilicueta’s pass and firing into the top corner. It rounded off a very satisfying evening’s work for Frank Lampard’s side, who next head to Selhurst Park on Tuesday.

Dominant start

In very light drizzle on a murky summer’s evening, Chelsea started authoritatively, pressing and probing the swarms of Hornets stationed behind the ball. Our first shot in anger came from a free-kick and the left boot of Giroud, smashed into the wall. Then Pulisic released Giroud whose cross was cleared.

That duo combined again on 17 minutes, and it took a fine low save with his feet by Ben Foster to keep the French striker’s driven effort out. He wouldn't have to wait much longer.

Not for the first time since the restart, the drinks break brought renewed energy and a goal for the Blues. Mason Mount worked it through the lines to Barkley, who slipped it into space for Giroud. He intelligently angled his first-time finish across Foster and in off the right-hand post.

The Blues kept their foot on the throttle. Pulisic looped a header into Foster’s arms, and the keeper then had more difficulty dealing with a delicious Reece James cross, uncomfortably fumbling it into a danger area. Luckily for him a visiting defender reached the loose ball first.

Pulisic has undoubtedly been Chelsea’s standout player since the restart, and it was his skill and speed at the end of another threatening dribble that culminated in our second goal. Etienne Capoue had no answer to his trickery, wiping the American’s feet from under him.

Just as against Manchester City and West Ham, Willian despatched his penalty with minimum fuss, although in contrast to those spot-kicks he opted for the top right-hand corner on this occasion.

It had been Chelsea’s most comfortable half since play resumed, and we merited a two-goal lead to show for our efforts. Aside from a couple of Watford crosses, the Blues defence had been untroubled.

In control

Pulisic was back in the thick of things when play restarted. Adrian Mariappa was booked for a foul on him, and then he nearly picked out Giroud after driving from deep and finding Watford gaps.

Chelsea kept coming. Giroud was denied by a combination of Foster and Craig Dawson after neat work from Willian, who himself stung the keeper’s palms with a trademark 20-yard curler. From his corner that followed, Kurt Zouma headed straight at Foster.

With a quarter-of-an-hour remaining, and moments after Watford’s first shot on target, Frank Lampard made his first changes of the evening, introducing Tammy Abraham, Ruben Loftus-Cheek and, for his maiden involvement since the restart, Callum Hudson-Odoi.

N’Golo Kante, who had been as tidy as ever in midfield, then limped off in some discomfort, Billy Gilmour the man brought on in his place.

Fitting finale

Kepa had easily held on to a couple of speculative long-distance Watford efforts, but with 10 minutes left he was at his very best, stretching low to his left to get a strong hand to Danny Welbeck’s effort after Nathaniel Chalobah had played the former Arsenal man in. It was Watford’s only clear opening all night.

In the closing stages, Pulisic had a penalty appeal waved away, and Loftus-Cheek misguided a header over from James’ teasing delivery. Will Hughes couldn’t convert Welbeck’s centre, and then a third goal did eventually arrive, Barkley turning and firing into the top corner for his first league strike of the season. It crowned another good individual performance from the midfielder, and a welcome three points with five league games now remaining.

The selection

After the midweek defeat, Lampard made four changes to his starting XI. James and Zouma were brought into the defence at the expense of Marcos Alonso and Toni Rudiger, Mount replaced the injured Mateo Kovacic, and Giroud came in for Abraham.

Penalty perfection

As well as his penalty giving the Blues some welcome breathing space, Willian made a little bit of history by becoming the first Chelsea player to net from 12 yards in three consecutive Premier League matches. Indeed, he is just the sixth player in the competition’s history to achieve that feat, and his latest successful spot-kick means he now has more Premier League goals and assists combined - 14 - than in any other previous campaign.

Staying in check

With Leicester and Manchester United winning earlier in the day, it was crucial Chelsea secured a victory tonight. We move back to within a point of the Foxes in third, and are two ahead of Man United in fifth. It is then another three points to sixth-placed Wolves following Arsenal’s victory at Molineux.

Chelsea (4-3-3): Kepa; James, Christensen, Zouma, Azpilicueta (c); Barkley, Kante (Gilmour 78), Mount (Loftus-Cheek 76); Willian (Hudson-Odoi 76), Giroud (Abraham 76), Pulisic.Unused subs Caballero, Rudiger, Alonso, Jorginho, Pedro.Scorers Giroud 28, Willian (pen) 43, Barkley 90+2

Watford (4-2-3-1): Foster; Mariappa, Cathcart, Dawson, Femenia (Masina 64); Capoue (Welbeck 58), Chalobah; Sarr (Pereyra 83), Doucoure, Hughes; Deeney (c) (Cleverley 64).Unused subs Gomes, Cathcart, Pedro, Gray, Holebas.Booked Capoue 21, Mariappa 49

Referee Kevin Friend