Fisher was released by the Exiles at the end of the 2013/14 campaign after spending six years at the club.
But after impressing during the summer the 26-year-old was signed on a full-time contract by the Saints. And as an ever-present in the match day squad so far in 2014/15 an early return to his old stomping ground was inevitable, as were the myriad of different feelings he had in the days leading up to the game.
“It was quite strange for me,” the flanker told BBC Radio Northampton. “It was definitely odd for me going into the away changing room! But I had to focus on the rugby - that was the most important thing - and not expend too much energy during the week leading up to today.
“For me it was about being a Northampton player, doing my best for the team and not worry about what has gone before.”
However while he had spent virtually all his professional career in the emerald green, Fisher said that there had been plenty of changes at London Irish since he had left the club.
“They are very much a different outfit to when I was here,” he admitted. “They’ve got new personnel and different strengths, and are trying to play a different way. I may have been able to bring some inside info into one or two players and what they like to do, but in the heat of battle you don’t wait for people to do things. You have to make it happen.
“We put in some consistent effort and scored a good try but left some more out there. We didn’t play particularly well, but to come here and get the win was a good effort.”
You can re-live the game at www.saintslive.co.uk
The Saints return home on October 11th to host Sale Sharks. Tickets are on sale right now; head to www.tinyurl.com/SAI-SAL-1415 and follow the straightforward instructions. Use [email protected] to beat the match day queues and save the admin fees!