Chelsea 4 – Southampton 2: Costa double helps Blues move seven points clear of Tottenham

Cahill missed Saturday’s FA Cup semi-final win over Tottenham with a bout of gastroenteritis, which left him in hospital for two days.

But at Stamford Bridge the England defender grabbed one of the most crucial goals of Chelsea’s season, with his header on the stroke of half time.

His side had seen their opening goal from Eden Hazard cancelled out by Oriel Romeu, but after Cahill restored order, Diego Costa nodded a third and right at the end grabbed a second – before Ryan Bertrand headed in a 90th minute Saints consolation.

Chelsea’s lead at the top is now back to seven points – and the pressure is back on Mauricio Pochettino’s Tottenham, in action at in-form Crystal Palace on Wednesday, and needing to win.

Conte had been stressing before the game that winning the title in England – or even the Double – would be the pinnacle of his career as player and coach so far.

And that coming from a man who won three successive Serie A titles with Juventus. 

The Italian had been bold at Wembley on Saturday, leaving Costa and Hazard on the bench, the ploy paying off as his team beat Tottenham to book a place against Arsenal in the FA Cup final.

On Tuesday, however, both were back, but again there was a surprise, with Cesc Fabregas deployed in a more forward role behind Costa .

It took only five minutes for Chelsea to make their mark. Fabregas found Costa, who held the ball up on the right and laid it back to Hazard, who slotted his right-foot shot into the far corner.

There were six Saints defenders around him but none got close.

It was Hazard’s 15th league goal of the season, his best return since joining Chelsea and it came against Claude Puel, the coach who gave him his chance as a teenager at Lille.

Costa then put Hazard away again as Chelsea broke once more with bewildering speed, but this time the Belgian lifted his shot over the bar. 

But Saints were not idle, several times looking dangerous down the right.

And when Conte’s team failed to clear a corner, Manolo Gabbiadini was all alone at the back post to knock the ball across and former Chelsea man Romeu slotted in the equaliser from point-blank range.

Right now, it seems, Chelsea cannot hold on to a lead – they let it slip twice on Saturday – and it meant 11 league games without a clean sheet for Conte’s team. Odd for a coach who is so insistent on organisation in his teams.

The nerves were showing at Stamford Bridge. Suddenly, all the swagger had gone. Conte was pacing his technical area and waving his arms frantically. Costa went down in the area but referee Lee Mason was having none of it, and then Nemanja Matic saw his shot def ected just wide.

At the other end though, Sofiane Boufal hit the side netting.

But on the stroke of half-time Chelsea were ahead again. 

Saints failed to clear another corner, N’Golo Kante swung the ball back in, Marcos Alonso nodded on and Cahill headed home.

Chelsea’s vulnerability down the right always offered Saints hope.

But equally, a defence that had given away 40 goals in 31 games suggested problems.

And it was 41 just eight minutes after the break, as Hazard fed Fabregas, and his chipped cross to the back post was met with a thumping header from Costa.

It was the rumbustious Spaniard’s first goal in eight games for his club. In truth his performance had been patchy at best.

But Costa has always been able to find the net, and it was a vital goal – at last putting daylight between Chelsea and their opponents.

Chelsea had obviously been given a rocket by Conte at half time, because there was much more energy and desire about them.

Even then, Gabbiadini still managed to hit the side netting, causing the Italian to boot a medical bag on the touchline in anger.

Then, with minutes remaining, Costa swerved through after exchanging passes with Pedro and Hazard, and slotted in his second goal. Job done.