Victoria Azarenka will take on Flavia Pennetta in the semi-finals of the US Open after breezing past Daniela Hantuchova.
The second seed had struggled in her previous two matches against Alize Cornet and Ana Ivanovic but she looked in better form under the lights on Arthur Ashe.
Azarenka got the better of three straight breaks of serve to start the match and pulled away to take the first set.
Hantuchova made a stronger start to the second, winning the first two games, but back came Azarenka with a run of five games in a row.
She suffered a minor blip when she was broken serving for the match, throwing in a double fault, but she hit back straight away to win 6-2 6-3 in an hour and 16 minutes.
Pennetta had earlier joined Serena Williams and Li Na in the last four by overcoming her fellow Italian Roberta Vinci 6-4 6-1.
Had Hantuchova won, all four semi-finalists would have been aged over 30.
Azarenka said: "I'm a baby, what can I say.
"It's amazing to see such great players in the semis. Flavia has been through such a lot and to see her doing so well is incredible and I can't wait to play against her.
"Everybody looks much fitter, everyone's really taking care of their bodies, and it's taken the sport to the next level."
Azarenka will be a big favourite to beat Pennetta, which could very well set up a final rematch against top seed Williams.
The pair met in a grand slam final for the first time here 12 months ago and it was a great battle, Williams eventually edging it.
Azarenka said: "I'm really excited to be in the semi-finals. New York is one of my favourite places to play. It gives me so much energy. Every time I want to go out and fight. I play like a kid here."
Pennetta continued her remarkable US Open run to reach her first grand slam singles semi-final.
The 31-year-old had made the quarter-finals in New York three times before but was well off the radar before the tournament began.
Initially, Pennetta was not even ranked highly enough to get into the main draw but crept in after a withdrawal.
The world number 83 is a former top-10 player but missed this tournament last year and the following six months because of a wrist injury.
She struggled when she returned to the tour, winning just three matches in her first seven tournaments and dropped out of the top 100.
But a run to the semi-finals in Strasbourg in May as a qualifier showed her form was coming back and she reached the fourth round at Wimbledon.
Pennetta said: "From the first day of the tournament I never thought I would be here and be talking about the semi-finals.
"I didn't play my best tennis in the last six months, and I just tried to keep working and working the same way every day.
"I'm starting to feel more my forehand, my backhand. Everything is starting to feel more normal in the way it was before the injury.
"I'm playing really good tennis here. Every day is much better. Every day was tougher and I've adjusted, tried to use everything I have and take it to the court and play my best tennis."
Pennetta had reached the last eight without dropping a set, beating fourth seed Sara Errani - another Italian - in the second round, former champion Svetlana Kuznetsova in round three and in-form Simona Halep in the last 16.
Pennetta and Vinci have known each other 20 years, and Pennetta admitted that made the match more difficult.
"I felt it a lot," she said. "I think in the beginning we didn't play good tennis. I was tight, she was tight also.
"When I won the first set I just relaxed a little bit and tried to play better. But the day was tough for both of us."
It has been a terrific tournament for the Italian women, with Vinci beating qualifier Camila Giorgi in the fourth round.
Pennetta will now attempt to become the first Italian to reach a singles final at Flushing Meadows.