Deadly Diego Costa is back and ready to kill Tottenham's title hopes
Heading into the clash at Stamford Bridge, the Spain international was in the midst of his longest barren run in front of goal since arriving from Atletico Madrid in 2014. For much of the first half, it seemed like that run may extend to seven games.
But when Cesc Fabregas floated a cross up to the back post, Costa was there to out-battle Ryan Bertrand and head home. A late second took him to 20 goals for the season. Suddenly things do not look so bad after all.
If Costa is back among the goals then Tottenham might as well give up on the title. Chelsea have had spells with Costa in-form and Eden Hazard in-form this season, but rarely both at the same time.
Hazard's fifth minute goal got Chelsea on their way on Tuesday, with Costa providing the assist - his first since 3 December against Manchester City. Hazard's finish was one of great skill but his real moment of genius was to make his goal celebration all about Costa.
That said, Southampton responded well, with Oriol Romeu equalising from one of a series of set-pieces that troubled the Chelsea defence. The time for leaders was now.
Chelsea without John Terry, however, are far from leaderless, with Cesar Azpilicueta stepping up by producing a 60-yard run to close down Southampton goalkeeper Fraser Forster. This served as a reminder to Antonio Conte's side that wins do not come easy.
This time last week, Gary Cahill was in hospital as he suffered a severe virus, but a week later he scored the a captain's header at the end of the first half. The momentum swung the game back into Chelsea's favour, and from there they needed just one more thing to cap off a perfect evening - a goal for Costa.
