The midfielder took just 10 minutes to show the skill that caught everyone’s eye during his loan spell at Swansea last term.
Andros Townsend burst down the left and cut the ball back to Gylfi, who controlled, shifted away from a couple of defenders and drove low into the far corner.
“It’s always nice to score, but the most important thing is to get used to playing football again and getting back to full fitness,” said Gylfi.
“It would be better to score in Premier League game, but nice to score my first goal of the season and have that confidence for the next couple of weeks.
“I’m off the mark, but it doesn’t really matter in the friendlies. There is no point scoring in the friendlies and not scoring in the league, so it’s about getting back to full fitness at the moment and we’ll see where we are at the start of the season.”