Wilshere was sidelined for almost 18 months with ankle and knee injuries before returning to action this season.
The 21-year-old continues to grow with every game and capped a man-of-the-match display to finally beat inspired Swansea keeper Michel Vorm with a 20-yard strike after 86 minutes to set up a trip to Brighton and keep alive hopes of Arsenal's first trophy since 2005.
"I didn't expect him to be this good at this stage," said Wenger.
"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 for me."
The Gunners were much improved from the lacklustre 2-0 Premier League defeat here by Manchester City on Sunday, and but for a combination of poor finishing and brilliant defending would have had the tie wrapped up before Wilshere's fine late effort.
With France striker Olivier Giroud returned to the starting line-up and Theo Walcott switched back to the right flank, Arsenal opened up full of movement - which had been lacking against City.
But more often than not, the finishing was lacking or Arsenal were foiled by brave defending.
"It was unbelievable that we couldn't score but we got it in the end. We persevered and we were rewarded," said Wenger.
Walcott was out of luck, seeing several goalbound efforts blocked, and should have been given a penalty when nudged over by Chico in the second half.
Wenger hopes a contract extension with the England forward can be pushed through sooner rather than later, and the Arsenal manager maintains that is his focus rather than heading into the January transfer market.
"Let's first try to finish the deal with Walcott," he said. "I hope it will be soon - very, very soon now."
All is not lost this season for Swansea, with Michael Laudrup's men looking to reach the League Cup final as well as consolidate their place in the Premier League.
Last night's tie could have been given a different complexion had a first-half header from former Gunner Kyle Bartley gone in off the bar.
"We tried, we defended well, at times heroic," said Laudrup, who made six changes and started with leading scorer Michu on the bench.
"You think it could have gone into extra time, but they deserved the win in the end. It is not a question of saying it doesn't matter, and I am disappointed."