Chelsea recovered from a shock early Southampton goal to win 3-1 and close the gap on Arsenal to four points again.
Stamford Bridge was silenced in the first minute of Sunday's Premier League clash when Jay Rodriguez punished a Michael Essien error to put Saints ahead.
But second-half goals from Gary Cahill, John Terry and substitute Demba Ba produced an emphatic turnaround and kept the Blues on the Gunners' heels.
Jose Mourinho made four changes to his side, with midfielders Juan Mata and Essien, striker Fernando Torres and forward Eden Hazard all starting. John Obi Mikel, Frank Lampard, Willian and the injured Samuel Eto'o were the
players who made way following the 1-0 Champions League defeat at Basel in midweek.
Saints showed two changes from the side which began last weekend's loss at Arsenal, with Dejan Lovren and Dani Osvaldo replacing Jos Hooiveld and Rickie Lambert.
The visitors took the lead after just 12 seconds as Essien's woeful attempted backpass went straight to Rodriguez 16 yards out and he tucked the ball past Petr Cech.
Essien's afternoon got worse when he was booked for diving just before the half-hour mark, and he was subsequently hauled off at half-time and replaced by Ba. Lampard came on for Oscar shortly before the break.
One of the last acts of the first half saw Hazard and Mata combine well to get in a cross which was met by a header from Torres that Artur Boruc kept out with a brilliant one-handed save going to his right, before the ball was hacked clear.
However, Chelsea did bring themselves level 10 minutes after the restart. Hazard's corner was met by Terry who headed goalwards and although Boruc did well to keep out a touch from Ramires, the ball broke to Cahill who headed in his first goal of 2013 from close range.
Boruc had to depart the action soon afterwards due to a finger injury, meaning Paulo Gazzaniga was summoned from the bench.
And the 21-year-old Argentinian goalkeeper was picking the ball out of his net just four minutes after his introduction. Mata's corner was headed out to Lampard on the edge of the box and he volleyed a pass back out to the Spaniard. His cross was met by a glancing header from Terry which found the top corner to mark his 400th Premier League appearance in style.
Chelsea's comeback was capped in the 90th minute as Ramires got in a cross that was met first time by Ba as he slid in and the ball found the corner of the net.
The result keeps Mourinho's men second in the table after 13 games played, four points behind Arsenal and two above third-placed Manchester City. Saints end the weekend in seventh spot.
Chelsea's assignments next week are at Sunderland and then Stoke, while Southampton host Aston Villa on Wednesday night before taking on City at St Mary's on Saturday.
