The 21-year-old - out for almost 18 months with ankle and knee injuries before returning to action this season - capped a man-of-the-match display to finally beat inspired Swansea goalkeeper Michel Vorm with a 20-yard strike on 86 minutes to set up a trip to Brighton and keep alive hopes of Arsenal's first trophy since 2005.
"Jack was outstanding," Wenger said.
"He played in a different position, a bit higher up and it suited him well. I didn't expect him to be this good at this stage. I always thought that if we could get Jack back to a reasonable level by January we will have done well, but he is ahead of what I could imagine.
"He is back to what he was before the injury, I think so, yes. A complete midfielder can defend and attack and Jack can also dribble and give a final ball so the closer players like him are to the goal the better it is for them. He has quality and enthusiasm and a love for the game, which is the most important thing for me."
Until Wilshere's goal the finishing was lacking or Arsenal were foiled by brave Swansea defending. Wenger added: "It was unbelievable that we couldn't score but we got it in the end. We persevered and we were rewarded. Overall we gave a good performance and it is important that we develop like that as a team. We were dangerous everywhere."
All is not lost this season for Swansea, with Michael Laudrup's men looking to reach the Capital One Cup final at Wembley as well as consolidate their place in the Premier League. This tie could have been different had a first-half header from former Gunner Kyle Bartley gone in off the bar rather than bouncing away.
"We tried, we defended well, at times heroic," said Laudrup, who made six changes to his side and started with leading scorer Michu on the bench.
"They had two or three chances where you say 'It's only a matter of time when they score'. If they score a few minutes from the end you think it could have gone into extra-time, but they deserved the win in the end.
"I want to win every game and the players want to, but it's not possible for anyone. It's not a question of saying it doesn't matter and I am disappointed."