Goals from Steven Davis, Sadio Mane and Graziano Pelle ensured that Southampton continued Chelsea's difficult start to the new Premier League season by securing a 3-1 victory away at Stamford Bridge.
Jose Mourinho restored John Terry to his starting lineup for the first time since mid September and elected to start with Falcao in attack as Diego Costa completed his three-match domestic ban.
Ex-Chelsea midfielder Oriol Romeu picked up an early yellow card against his former side for a foul on Eden Hazard, and the hosts took immediate advantage to open the scoring as Willian curled home.
Davis missed a chance to equalise for Ronald Koeman's side after he was given a sight of goal but could only fire into the side-netting, before Oscar fired over as both sides looked for the second goal of the game.
Southampton began to dominate the home side in the final 10 minutes of the half and could have levelled when ex-Blue Ryan Bertrand failed to beat Begovic when one-on-one.
That was a let-off for Chelsea, but it was a warning sign that they failed to heed as a minute later Davis equalised in spectacular fashion, Pelle chesting the ball to the Northern Irishman, who crashed a first-time volley past Begovic from outside the box to restore parity before the whistle.
The Saints came out of the traps quickest in the second period and they almost stole the lead through Mane, who was first denied by Begovic and then by a retreating Terry.
Mane had the last laugh, however, when the striker was later played in by Pelle before turning Terry adroitly and firing his shot down low past Begovic in the hosts' goal to make it 2-1.
Things grew even more troublesome for Mourinho's charges in the 72nd minute, when Mane broke away on the counter to feed Pelle, who proceeded to add the away side's third goal of the evening with a drilled finish past the keeper.
The current champions might have finished the game three goals shy of their opponents had Dusan Tadic been a touch more efficient, but he could not find a way past Terry's block despite some incisive passing from an inspirational Mane late on.
