The Iceland midfielder came off the bench in the 56th minute and with his first touch, forced inspired goalkeeper Jussi Jaaskelainen to tip a curler onto the post.
That was typical of Gylfi’s luck in front of goal this season.
It’s been a case of so near, so far for Gylfi including striking the crossbar against Everton at Goodison Park and then seeing Asmir Begovic somehow save a goalbound header late on in the goalless draw against Stoke.
But that all changed in the 76th minute. Gareth Bale whipped in a free-kick and the ball bobbled around in a scramble before landing at the feet of Gylfi, who slotted home from close range to level the scoreline at 2-2.
Having dominated and forced Jaaskelainen into a string of fine saves, Gylfi’s goal provided the final spark for us to go out and win the game, the victory secured by another superb strike from Gareth into the top corner from 30 yards in the final minute.
The result made it 11 unbeaten in the Premier League, stretched our run to one loss in 15 and moved us into third place.
“That goal has been a long time coming,” said Gylfi. “I’ve hit the post a few times and the bar so it was a good feeling, especially in a game like this, a London derby.
“Even at 2-1, we always believed we could get back into it, the game was open, a lot of chances, a lot of shots and it was important to get that goal when we did so we still had time. Gareth then scored that unbelievable goal right at the end.”
You could have excused Gylfi for thinking 'here we go again' when his first effort was touched onto the post by Jaaskelainen.
“That’s when I started thinking it was going to be another one of those games,” he added. “He was fantastic, made a few saves particularly from Steven Caulker and it looked like it wasn’t going to be our night.
“Finally, I got that goal and I was delighted with that.
“It meant a lot to us and being able to go ahead of Chelsea, that’s fantastic and we have to keep going now and maintain this momentum.”