Olivier Giroud came off the bench to score twice as Chelsea came from two goals down to beat struggling Southampton 3-2 and keep alive their hopes of Champions League qualification.
The home team went ahead thanks to Dusan Tadic's fourth Premier League goal of the season (21), before Jan Bednarek volleyed home a second on his top-flight debut (60).
However, the champions responded in style by scoring three times in only nine minutes via a stooping header from substitute Giroud (70) - his first league goal for Chelsea - before Eden Hazard's composed finish brought them level (75).
Then with 12 minutes to go Giroud completed the comeback with a low drive to inflict a fourth defeat in a row on the struggling Saints.
As a result, Southampton remain in the relegation zone, while Antonio Conte's team, after their first two-goal comeback since 2002, moved to within seven points of both Tottenham and Liverpool - who play later today - in the race for the top four.
Southampton had opened the scoring after 21 largely uneventful minutes following a lovely build-up down their left flank involving Ryan Bertrand, sent clear by Pierre-Emile Hojbjerg's inch-perfect pass.
The England left back then got the better of Cesar Azpilicueta in a foot race, before pulling the ball back for the waiting Tadic to nip in front of his marker and side-foot the hosts ahead with his first strike since Boxing Day.
It took a flat Chelsea - fortunate not to see Marcos Alonso sent off for a late tackle on Shane Long just before the break - until the second half to test Alex McCarthy.
The Saints No 1 just did enough though to keep out Willian's low drive from the edge of the area, minutes after Thibaut Courtois also had to be alert to touch over Long's looping effort.
However, Mark Hughes - taking charge of Southampton at St Mary's for the first time - only had to wait till the hour-mark for his side to double their lead, and it came via an unlikely source.
James Ward-Prowse floated a free kick to the far post for Bednarek to cushion a volley past Courtois as a first league win under their new manager appeared to be on the cards, only for the visitors to hit back with three goals in only eight minutes.
Giroud, only just off the bench, headed in Alonso's inch-perfect cross from the left, before Hazard kept his cool to trap Willian's cut back and drill the Blues level as Southampton heads dropped.
And the France international then sealed a quite remarkable turnaround by firing through a posse of Saints defenders to keep Chelsea's Champions League hopes alive.
Match stats
- Southampton have lost consecutive Premier League games after scoring 2+ goals for the first time ever
- Hughes is only the second manager to lose three Premier League games against the same opponent in a single season after Graeme Souness vs Arsenal in 2004-05
- The Blues have won five in a row against Saints in the league for the first time ever
- Tadic has been directly involved in 45 Premier League goals since his debut in August 2014 (18 goals, 27 assists), 14 more than any other Southampton player.
- Bednarek is only the third Polish player to score in the Premier League, after Robert Warzycha in 1992 and Marcin Wasilewski in 2015
- Giroud is the top-scoring sub in the Premier League this season, with six goals from the bench
- Giroud is the first player to score an away goal against the same opponent for different clubs in a single Premier League season since Mikel Arteta (for Everton and Arsenal v Blackburn 2011/12)
- Hazard has scored 69 Premier League goals for Chelsea; only Frank Lampard (147) and Didier Drogba (104) have netted more.
The managers
Mark Hughes: "For the most part I was pleased with what I was seeing, I saw a team that was committed to what we are trying to do.
"That was evident and we got ourselves into a great position, a winning position because we should have seen the game out, but we've got a soft underbelly which we've had all year apparently.
"Shane's got a gash down the calf, having seen it again there's a clear red card. There's clear intent to hurt Shane, it was raked down the back of the calf, it's a dangerous tackle and could have broken his leg."
Antonio Conte: "Our first half wasn't good, in a lot of aspects. I think we didn't show great spirit, enough desire or will to fight for a good result. The first-half was very negative.
"I saw a great reaction after half-time, the right will to fight, the right desire to win this game, despite the difficulties because they went 2-0 up.
"If you don't have something in your heart, it's very difficult to win the game, but today I'm very happy with the second half, and very disappointed with the first.
"I'm the first to take the fault for the first half, but I repeat the second half my players deserve great credit."
Pundit - Dennis Wise
"This is a joke by Mike Dean (not to send Marcos Alonso off)," he said. "He knows what's gone on, he's turned a blind eye to it. He'll turn round and say I never saw it. If he never saw it, he one shouldn't be refereeing and should have glasses.
"That's a red card. He hasn't even bothered with the ball. The thing about it is Ward-Prowse got booked, he realised what Alonso had done to Long and reacted to it."
Man of the Match - Olivier Giroud
The forward, who joined Chelsea from Arsenal in January, entered the contest on the south coast just past the hour-mark, and it took him next to no time to turn the encounter on its head.
His first was a trademark bullet header, before the Frenchman won the points for the Blues with a low drive into the corner of the net, his 19th Premier League goal as a sub.
And that means the 31-year-old is now just five behind Jermain Defoe's record for most goals off the bench.
What's next?
The Saints take on Leicester City at the King Power on Thursday evening, while Chelsea are also in action that night with the champions facing a tough-looking trip to high-flying Burnley.
And both teams then meet each other again in the FA Cup semi-finals at Wembley on Sunday April 22.