The 24-year-old made his Lions debut Down Under, featuring in the fixtures against the Brumbies and Melbourne Rebels after flying all the way from Buenos Aries where he was on international duty with England.
Gloucester were staring their worst ever start to a Premiership season in the face in the closing stages of their encounter with Northampton Saints but a late penalty presented Twelvetrees, who also grabbed a first-half try, with the chance to be a hero.
And after sinking the kick to record a thrilling 26-24 victory, Gloucester director of rugby Nigel Davies insists Twelvetrees showed great composure to come through when it really mattered.
"Billy [Twelvetrees] will know he had a mixed bag, but ultimately he came through strong. He had the confidence in himself to nail an absolutely crucial kick for us to get our season under way," said Davies.
"More importantly, from my perspective, I felt that overall we deserved to win with the performance we put in.
"What is important is that we got the win. It was a very exciting game with a very dramatic ending to a fabulous match."