Chris Robshaw also got in on the act for England with an opportunistic effort, but it was Farrell - who came off the bench in the vital third Test decider Down Under which the Lions won 41-16 - who impressed.
There was an element of doubt surrounding the try as Dylan Hartley appeared to block Stephen Moore, but Farrell insists it was a legitimate try and one which capped a deserved victory.
"I had a look outside me first, then you have to check if there is a space in front of you and I saw a little gap open up and thankfully I took it," said the 22-year-old.
"I just think Dylan was trying to get back, obviously he had run a line before that and he was making his way back.
"He was just going straight, he didn't step across anybody so it wasn't obstruction."