Chelsea 3 Watford 0

It took a couple of half-time substitutions and, perhaps, a dressing room dressing-down from José Mourinho, but Chelsea eventually cruised into the fourth round of the FA Cup thanks to a trio of second-half goals. After a first period in which Watford had laid the groundwork for an upset, the introductions of Diego Costa and Willian helped turn this tie in the favour of the team at the top of the Premier League, with goals from William, Loïc Rémy and Kurt Zouma giving the scoreline a comfortable appearance.

Any of the 6,000 Watford fans who had made the short journey to Stamford Bridge fearing their team would be made to pay for Chelsea’s New Year’s Day thrashing by Tottenham must have been soothed by the obliging start made by the hosts and the dynamic one by Slavisa Jokanovic’s men.

Chelsea, fielding just three of the players who began against Spurs, were sluggish and sloppy from the outset, while Watford were solid and tenacious in a 4-5-1 formation and carried a promising threat on the counterattack.

The upstart visitors were even the first to force the opposing goalkeeper into action, as long-range shots from Daniel Tozser and Troy Deeney drew saves from Petr Cech. Deeney offered a pleasing vignette of Watford's attitude in the 22nd minute, when the striker chased back 60 yards to deny Oscar with a perfectly timed slide tackle after a Watford corner had been cleared.

Chelsea did not hint at scoring until the 29th minute, when Rémy produced a fine cross from the right and Didier Drogba outjumped Craig Cathcart at the near post but headed just over the bar. Drogba showed his menace again four minutes later, when, after a sublime piece of chest control, he teed up André Schürrle for a clear shot at goal from 18 yards. But the German World Cup winner hit a wonky effort into the stands.

Fernando Forestieri’s end product was proving equally unsatisfactory at the other end, which was a shame as the Italian was otherwise highly promising, regularly beating César Azpilicueta down the left.

Gary Cahill threatened to give the hosts a half-time lead that their tame play hardly merited, but headed narrowly wide from a corner in the 42nd minute. On the stroke of half-time Odion Ighalo dragged badly wide from the edge of the Chelsea box after another sharp counterattack from Watford.

Slavisa Jokanovic must have been satisfied at half-time that his plan was broadly on track. Mourinho, on the other hand, can only have been alarmed at his side’s somnolent display. He made a pair of substitutions during the break in a bid to wake his team up, Costa and Willian replacing Oscar and Schürrle.

Watford, scenting a famous triumph, were not about to surrender the initiative. They continued to fluster their illustrious hosts, frequently winning battles of muscle and sharpness. Deeney offered another prime example in the 55th minute when he ambushed Mikel John Obi in the Chelsea box before seizing the ball and sending in a cross that Felipe Luís deflected just wide of his own goal.

Moments later Drogba brought a save from Bond after racing on to a deflected cross by Costa. Then, in the 58th minute, the substitutes did what Mourinho had unleashed them to do, shattering the deadlock with a flash of much-needed ingenuity. Costa, whose movement was beginning to tear holes in the visiting defence, foraged down the right before offering Willian a shooting opportunity from 20 yards.

The Brazilian seized it with style, curling the ball into the top corner.

If they had struggled to gain the lead, Chelsea never looked like relinquishing it. Their grip on the game already seemed ominously imperious before they secured victory with a second goal in the 70th minute. Again Costa was instrumental in the creation. After a one-two with Drogba he unleashed a shot from 15 yards that was blocked by a defender before the ball dropped to Rémy, who walloped it into the net on the volley from 12 yards.

Zouma's headed goal two minutes later hardly affected the outcome but did serve as extra recompense for a 20-year-old defender who deputised well in place of John Terry in Chelsea's defence.

Cech's late one-handed save from a 20-yard drive by Matej Vydra denied Watford a goal to reward their gallantry. Bond then had to repel a Costa free-kick to prevent Chelsea inflicting more damage.