Caroline Wozniacki kept her hopes of a first Grand Slam title alive with a brilliant win over Svetlana Kuznetsova to reach the US Open quarter-finals.
The world number one was in desperate trouble at a set and 4-1 down but battled back to win 6-7 (6-8) 7-5 6-1.
It was a magnificent effort and the Dane goes on to face 10th seed Andrea Petkovic of Germany in the last eight.
Three-time champion Serena Williams earlier produced a dominant display to beat Serbia's Ana Ivanovic 6-3 6-4.
But it was the night session encounter that proved the high-point of the women's event so far as the defensive skills of Wozniacki went head-to-head with Kuznetsova's more attacking style.
Wozniacki had won in a final set tie-break when the pair met at the same stage two years ago but it looked as though the Russian would prevail relatively comfortably this time after she hit back from 5-2 down to take the tie-break and moved 4-1 clear in the second set.
However, Wozniacki showed all the tenacity that has taken her to the top of the rankings, reeling off four games in a row and serving out the set at the second opportunity.
The Dane made three unforced errors to Kuznetsova's 29 in the second set and her greater fitness and consistency proved the difference as the Russian began to flag, dropping serve at the start of the third as Wozniacki went on to win in three hours and two minutes.
Wozniacki said: "I thought about the match we played against each other here in 2009. I was a set and break down in the second in that one and still won.
"I knew I could come back so I just stepped into the lines, went for my shots, and tried to make fewer errors. I am in good shape. I can play for five hours if I have to. I just wanted to keep the rallies going."
Williams, seeded 28th, was not at her very best in the afternoon session but was never really threatened by Ivanovic, who sent down two double faults in her opening service game as her high ball toss suffered in windy conditions.
"It was crazy," Williams said. "I didn't even go for winners at any point. I just tried to get it over because it was so windy. It was like, 'Wow'. It was definitely tough. It just kind of swirls down there. But you just have to win in all kinds of situations."
Ivanovic stayed calm and broke back in the fifth game when Williams made two unforced errors to bring the match back onto serve but the American stepped up a gear from 3-3 to close out the set.
Williams took an early 2-0 lead in the second and, although Ivanovic occasionally produced the goods, taking the third game with a thunderous ace, a missed backhand volley in the fourth allowed Williams to slam down of her own an ace to seal the game.
The American had only dropped six points on her first serve up until that point, winning 80% of the points behind it, and there was nothing Ivanovic could do to derail the former champion.
"My serve broke down a little more than hers," said Ivanovic. "I still created lots of opportunities and I felt I was stepping up a lot and I just felt that was the biggest difference today.
"As I said even before the match, I think she's the favourite for the tournament."
Williams still found plenty to work on from her performance, saying: "I think there's so much I can do better.
"I think, to be honest, the last two matches I wasn't completely satisfied with the way I played. I felt like I could have played a lot better, so there's a lot I can improve on."
She next faces Anastasia Pavlyuchenkova after the 20-year-old Russian beat Italian seventh seed Francesca Schiavone 5-7 6-3 6-4, while Germany's Petkovic defeated Spaniard Carla Suarez Navarro 6-1 6-4.