In-form fifth seed Casper Ruud pushed past Italian Matteo Berrettini 6-1 6-4 7-6(4) to reach the U.S. Open semi-final on Tuesday with a shot at the world number one ranking still on the line in New York.
The French Open runner-up beat Berrettini on clay in July's Gstaad final and looked just as effective on the hard court, hanging back behind the baseline to absorb the 13th seed's power.
Sprinting through a sublime first set in which he produced just two unforced errors, it looked like Ruud was on track for a blowout victory when he was up 5-1 in the second set.
"Everything sort of went in my favour. I was hitting all the spots, all the shots that I needed to. Matteo was maybe not showing the level he typically does," said Ruud.
But Berrettini, who was sidelined a number of times this season due to injury or illness, slowly began to find his usual level and appeared to have cracked the code in the third set when he broke Ruud in the second game and saved four breaks in the third.
Ruud mustered a terrific comeback, breaking Berrettini in the ninth and never trailed in the tiebreak.
"That was (a) better start than I ever had before in a match," Ruud said in an on-court interview, adding that he had to temper his enthusiasm in order to clinch the affair.
"Sometimes you can get a little overexcited and think you can walk on water," he said.
He and third seed Carlos Alcaraz have a chance at seizing the world number one ranking at Flushing Meadows, as current holder Daniil Medvedev crashed out in the fourth round.
"Of course it's a little bit (more) motivation," said Ruud. "I'm trying to go for it, of course."
Berrettini, who beat Ruud in the third round in New York two years ago, said the Norwegian had clearly upped his level.
"I think his return, definitely (has improved). Also his serve. He's able to mix it up," he told reporters. "He's more complete."
After being forced to miss the Australian Open when he rolled his ankle a day before the tournament, Ruud showed he can be a threat on hard courts when he reached the Miami final and Montreal semi-final this year.
"I'm honestly a bit surprised that I made it to the semis here, but I think I have developed my hard court game a lot the last year or two," he told reporters.
"Miami this year showed me and I proved to myself that I can beat good players and reach later stages in big hard court tournaments."