Jose Fonte admitted it was tough making such a swift return to Southampton.
The Portugal defender spent seven years with Saints before opting to join West Ham in the January transfer window.
A fortnight later he was back at St Mary's helping the Hammers to a 3-1 win on Saturday and piling on the misery for his old side.
"It was a strange experience coming back to Southampton," Fonte said.
"It was emotional, difficult, but in the end I can say a big thank you to everyone - to the West Ham supporters and my team-mates for helping me get through it.
"I managed to block everything out and stay focused on the game. The most important thing was achieved, which is the three points and a great performance."
West Ham fell behind to a debut strike from Saints' Italian striker Manolo Gabbiadini.
But Andy Carroll hauled the visitors level and Pedro Obiang's first goal for the club put them ahead at half-time, before Mark Noble's free-kick was deflected into his own net by Steven Davis.
It was the perfect response from Slaven Bilic's side after they were thrashed 4-0 at home by Manchester City three days earlier on Fonte's debut.
"It's never easy. That wasn't the start I wanted, we weren't at the races, but we showed great character and personality to come and play," added Fonte.
"We played some great football, scored three goals and could have scored a couple more. It was a fantastic performance from everyone and we move on to the next one."
Southampton's problems are piling up both on the pitch, where they have lost six of their last seven matches, and in the treatment room.
Key defender Virgil van Dijk is out for up to three months and on Saturday record signing Sofiane Boufal limped off, making him a doubt for the EFL Cup final against Manchester United on February 26.
"It's an ankle injury and we will see how long he stays out, I hope it's not important, we will see," said Southampton manager Claude Puel.
"He's an important player for us and we hope he will be available."