City made 10 changes from the side that was beaten by Chelsea at the weekend, with the Romanian brought in to replace the struggling Joe Hart, who was largely accountable for the goal that cost his side a point at Stamford Bridge.
The 26-year-old Pantilimon, who joined City in 2012, pulled off several fine saves to keep the score at 0-0, forcing the Capital One Cup fourth-round tie to go to extra time.
And Sky Sports expert Niall Quinn believes the keeper has taken the opportunity to prove himself in excellent style.
"It was more than a good impression from Costel Pantilimon," he said.
"I think he's given his manager a headache now ahead of this weekend. I don't buy the argument that Joe Hart was dropped, I think this player would have played anyway and he's taken that chance really well.
"When Newcastle had that dominance, he was absolutely unbeatable and he made the game so much easier for his team-mates."
In extra-time, City showed their strength and tapped in to their plentiful bench of stars who came on and made difference with Alvaro Negredo netting the first and then fellow substitute Silva setting up Edin Dzeko for the second.
Quinn said Pantilimon's performance will give the City manager a selection dilemma but with such a quality squad, he's always going to have big calls to make.
"Pellegrini has now got to think about it [playing Pantilimon instead of Hart] but I don't think it's a foregone conclusion," Quinn added.
"He's going to have to look at who he's playing at the weekend and say 'OK, it's Norwich and a home game, they won't be putting as much pressure on us, will I stick with my man?'
"It's a manager's duty, but it's a great thing. He made 10 changes tonight and brought in a whole new team. His bench was incredible tonight, he's got decisions like that to make and he'll be making them for years to come.
"This is his first test and Joe Hart will be hoping he sticks by him but that guy Pantilimon with what he's done tonight, he's made it really difficult to be dropped at the weekend."