The Saints got the better of Chelsea 3-1 away from home in the Premier League on Saturday evening.
Willian put the Blues in the lead at Stamford Bridge as early as the 10th minute from a free kick, but Southampton restored parity through Steven Davis two minutes before the half-time interval.
Sadio Mane made it 2-1 to Koeman’s side on the hour mark, and Graziano Pelle wrapped up the three points with his goal in the 72nd minute.
Over the course of the 90 minutes, Southampton had just 39% of the possession, took 13 shots of which five were on target, and earned six corners.
The Saints are now ninth in the Premier League table with 12 points from eight matches, just three points behind fourth-place Leicester.
Koeman was overjoyed with Southampton’s win against Chelsea and posted the following message on Twitter: