NEW YORK • From the anonymity of the first round of qualifying to likely star billing in the Arthur Ashe Stadium against two-time Wimbledon champion Petra Kvitova, the US Open fairy tale of Johanna Konta just gets better and better.

Konta added Germany's 18th seed Andrea Petkovic to her growing list of victims to move into the the fourth round of a Grand Slam for the first time with a 7-6 (7-2), 6-3 victory.

With an impressive list of scalps this year, including two wins over Wimbledon finalist Garbine Muguruza and another against fellow fourth-rounder Ekaterina Makarova, Konta appears to be unconcerned by the reputation of her opponents.

Now the Australian-born Briton moves to a different level against Kvitova, the world No 4. Although Konta was found wanting against Maria Sharapova at the All England Club, her confidence has returned since then with a winning run of 16 matches.

She has also showed remarkable powers of physical recovery.

Her marathon win in three hours and 23 minutes over Muguruza in Thursday's searing heat entered the record books as the longest women's match played in the tournament since tie-breaks were introduced 45 years ago. Yet, when the sun returned on Saturday, it was Konta's opponent again feeling the heat, with Petkovic calling a medical time-out after going down a set and 0-3 in the second.

Trainers checked the German's blood pressure and wrapped her in ice packs and ice towels and she offered up a brief fightback.

Up 5-1 and serving for the match, Konta could not put away Petkovic at first opportunity as the German broke and held serve. But Konta would not let Petkovic off the hook a second time, serving out to clinch the upset.

"To be honest, I feel just as I did two weeks ago, I haven't exactly grown wings or anything," said Konata, who arrived in New York ranked the world's 96th best player and is now destined for a place around 60th, or better, on the WTA computer.

She is also guaranteed prize money of at least US$213,575 (S$304,117) - not bad for someone who picked up US$392 in one of her early-season tournaments.

"I must say I'm happy with how I have been playing so far this week but my feet are firmly on the ground. I haven't cured cancer or anything."

But she is one win shy of equalling American Barbara Gerken's 1981 quarter-final run as the best in US Open history by a women's qualifier.

Kvitova, a 6-2, 6-1 winner over Slovakia's Anna Karolina Schmiedlova, admitted she knew very little about Konta, other than the fact she is unbeaten since Wimbledon.

"I've never played her so it's going to be something new," said the Czech. "Players don't get to the fourth round without playing well so it's going to be really tough for me."

Konta's compatriot Andy Murray advanced to the fourth round of the singles with a 6-3, 6-2, 7-5 win over Brazilian Thomaz Bellucci.

Murray, who won his first Major at the 2012 US Open a year before winning Wimbledon, had fought back from two sets down to beat France's Adrian Mannarino in the second round after needing four sets to beat Australian Nick Kyrgios in his opening match.

Meanwhile, Roger Federer continued to ease past opponents. His efficient 6-3, 6-4, 6-4 third-round victory over Philipp Kohlschreiber means he has yet to drop a set at Flushing Meadows this year.

THE TIMES, LONDON, REUTERS

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