Serbian qualifier Aleksandra Krunic ran third-seeded Petra Kvitova out of the US Open on Saturday, surprising herself as much as the Wimbledon champion.

Serving for the match at 5-4 in the second set, the 21-year-old world No.145 caught Kvitova flat-footed with a perfectly timed drop shot to take a 40-0 lead.

“I was like, ‘Oh, my God, I have triple match point! Maybe I can really win it,'” Krunic said, adding that she was still trying to absorb the fact of her second-round victory over American Madison Keys.

“It’s like so many things happening in my mind.

“I’m trying to believe it, but when I believe it I’m afraid that I’m going to have so much emotions. So I’m trying to keep it all together.

“My coach is already screaming and jumping, and I’m trying to stay away from him so I don’t listen,” she said, holding up her hands as if to ward off the excitement.

The pint-sized dynamo made the most of her 1.63m frame, making up for her lack of power with sheer determination.

“I didn’t really expect how she played so well,” admitted Kvitova, whose second Wimbledon title in July was followed by a couple of lacklustre results before she lifted the trophy in New Haven on the eve of the Open.

“Suddenly she just pushed very hard the ball. It was just coming so quickly then, so it was really difficult. I just didn’t really to have an answer for it.”

Krunic’s game plan, to extend the rallies and try to push Kvitova into mistakes, worked to perfection. The 24-year-old Czech committed 34 unforced errors and surrendered her serve five times.

But Krunic, whose second-round win over Keys was her first against a top-30 player, seemed astonished that she’d pulled it off against a player she was pulling for in two Wimbledon finals.

“I like Petra a lot as a person,” Krunic said.

“She’s very down-to-earth and I respect her a lot.

“I like when I can say hi and talk to the players that are much higher ranked than me and I don’t feel such a difference in our levels.

“Because still we’re all human beings.”