LONDON — Diego Costa ended a seven-game goal drought in style to help Chelsea open up a seven-point lead in the Premier League with a 4-2 victory over Southampton on Tuesday.

The second-half double halted a barren run that began shortly after a reported dispute at the club as Costa was linked with a move to the financially-flush Chinese Super League.

Even as the goals dried up and the uncertainty about Costa's future persisted, manager Antonio Conte never doubted his striker's ability to make an impact in the title run-in.

"For the forward it's very important to score ... because the goal is your life," Conte said. "But for me I always said that I'm very pleased for his commitment, for his work for the team, because he's always working for the team."

Costa was heavily involved as early as the fifth minute at Stamford Bridge when he set up Eden Hazard's opener. After Gary Cahill restored Chelsea's lead, Costa scored two contrasting goals in the second half.

The striker's 50th Premier League goal was a header from Cesc Fabregas' cross and his next goal was the culmination of a mazy run through the defence that saw him exchange passes with Hazard and Pedro Rodriguez.

Those goals helped the league leaders nudge closer to regaining the trophy from Leicester, having had their advantage trimmed in recent weeks by Tottenham. Second-place Tottenham is now on the back foot as it prepares to play Crystal Palace on Wednesday.

But one potential obstacle to Chelsea's winning the title on the five-match final stretch remains the leaky defence that had been so sturdy earlier in the season. Both Southampton goals came from former Chelsea players, with Oriol Romeu and Ryan Bertrand making it 12 league games since Conte's side kept a clean sheet.

Romeu's cancelled out Hazard's opener. Manolo Gabbiadini was left unmarked to bring down James Ward-Prowse's corner at the far post and strike at Thibaut Courtois. The goalkeeper parried the shot but the ball fell to Romeu for a simple tap-in. Chelsea was already 4-1 in front when Bertrand rose above Cahill to head in a cross from Cedric Soares.

"When you keep a clean sheet, it's a great achievement for your team," Conte said. "I think this situation we have to improve. We have to continue to work and try to improve our mistakes."

And yet the west London club seemed so relaxed about its advantage that captain John Terry had been brought on for his first league appearance since November and first since announcing he would be leaving at the end of the season.

It's likely that one of Terry's last acts of a 22-year association with Chelsea will be to lift the Premier League trophy. There could also be an FA Cup to collect if Arsenal can be overcome in the final. Conte gambled against Tottenham in Saturday's semifinal by starting without Costa and Hazard. It paid off at Wembley and the effects were felt by Southampton as the refreshed duo unsettled the Southampton defence.

"My choices were right for the game against Tottenham and the game against Southampton," Conte said. "It's not easy to make these strong choices. I have squad full of great men and good players."

The contribution of Fabregas shouldn't be overlooked. It was the midfielder's long defence-splitting pass that was cutback to Costa into the path of Hazard for the opener. The former Arsenal playmaker also whipped in the cross eight minutes into the second half that was nodded in by Costa. It was Fabregas' 103rd Premier League assist, overtaking former Chelsea midfielder Frank Lampard in a ranking that is topped by retired Manchester United great Ryan Giggs on 162.

Conte, after helping Chelsea recover from its loss to United in the previous round, now takes his team back to northern England to face Everton.

"We passed a big step, a big psychological step, after the defeat against United," Conte said. "Our answer was very good and for this reason I must be pleased."