Williams followed up his bonus point claiming try in Toulon last week with his 15th Heineken Cup touchdown to mark his 50th appearance in the tournament.
"The try makes everything better, but it was the win that was the most important thing after a disappointing defeat in Toulon," said Williams.
"We were under pressure to come out and perform because if we had lost it would have been the end of our campaign and it would have been all doom and gloom. They fought right to the end to get the bonus point and the fact they didn't get one was like a bonus point to us in the end.
"It was a very tough game and we were under a lot of pressure to play well. They played for the bonus point and we kept them out and I'm very proud of the way the players responded.
"I've found it very difficult to get involved in games recently because they have been so tight. It has been a little bit of nerves and not wanting to let people down around you.
"But I felt sharp out there and I just wanted a crack. I had two opportunities and I was disappointed not to score the first time.
"I knew I couldn't go around or through Topsy Ojo, so I tried to hurdle over him. But then I got creamed from the side and lost the ball.
"I feel pretty good at the moment and I certainly don't feel my age - and I'm not going to tell you my age. My rugby is going well and I'm happy.
"That was a great overall performance and I'm just happy we have been a very good London Irish side."