Russia's Anastasia Pavlyuchenkova battled back to defeat seventh-seeded Italian Francesca Schiavone 5-7, 6-3, 6-4 to reach her first US Open quarterfinal on Monday in a mistake-plagued last 16 clash.
Pavlyuchenkova, the 17th seed, triumphed in a match-up of the youngest and oldest players left in the women's draw and next faces either three-time champion Serena Williams or Serbia's Ana Ivanovic for a semifinal spot.
But Monday's 2hr 42min clash, which opened the Arthur Ashe Stadium programme on Labor Day, a national holiday in the US, was not for the purists with 21 double faults, 16 breaks of serve and a combined 95 unforced errors.
"It's a dream come true for me to reach the quarter-finals here for the first time. I'm so happy about it," said Pavlyuchenkova, who lost to Schiavone at the same stage last year and in the quarter-finals of this season's French Open.
The 20-year-old needed three match points to secure victory after squandering two with a pair of ugly forehands before a booming forehand winner wrapped up the affair.
With two-time defending champion Kim Clijsters not playing, and with former winner Maria Sharapova, Wimbledon victor Petra Kvitova and French Open titlist Li Na all losing before the third round, Williams is now the favourite.
The American, seeded down at 28 after a year spent battling injury and life-threatening blood clots, has won both her career matches against Ivanovic, a former world number one and French Open winner.
Ivanovic has yet to reach the quarter-finals of the US Open.
The day's other last 16 ties see top seed and world number one Caroline Wozniacki tackle 2004 champion Svetlana Kuznetsova, the Russian 15th seed.
Wozniacki, still without a Grand Slam title, was the runner-up to Clijsters at Flushing Meadows in 2009, beating Kuznetsova in the fourth round on her way to the final.
The Dane has a 4-2 winning record over the 26-year-old Kuznetsova. The winner of that tie will take on either German 10th seed Andrea Petkovic or unseeded Spaniard Carla Suarez Navarro.
Petkovic lost the pair's only other previous meeting at the 2010 Australian Open.
The German, who will be 24 on Friday, is bidding to reach her first US Open quarter-final having made the last eight at the Australian Open and at Roland Garros this year.
The remaining women's quarterfinals line-up was decided on Sunday with Vera Zvonareva, the second seeded Russian and runner-up last year, setting up a clash against Australian Samantha Stosur, the ninth seed.
Italian 26th seed Flavia Pennetta will be facing unseeded German Angelique Kerber in the other last eight tie.