New York: John Millman's joy was tinged with guilt after he stunned 20-time Grand Slam champion Roger Federer to reach the US Open quarter-finals on Monday.
As Federer struggled in suffocating humidity, his physical troubles contributing to 77 unforced errors, Brisbane-born Millman gained in strength to close out the contest 3-6, 7-5, 7-6 (9/7), 7-6 (7/3).
"I felt a little bit guilty today because he didn't have his best day today that's for sure," said Millman, a 29-year-old ranked 55th in the world.
"I'm very aware he didn't have a great day in the office. Probably to beat him I needed him to have an off day and I needed to have a good day."
Millman, in the last 16 of a Grand Slam for the first time, admitted to feeling like "a deer in the headlights" in the first set, but he rose to the occasion on the 23,000-seat Arthur Ashe Stadium court.
"It was a slightly intimidating environment," he said. "At the start I don't think I was playing so well. But as the match went on, I felt more comfortable, felt pretty good.
"I've always done a good job of not letting the moment get the better of me," added Millman, whose career has been slowed by a string of injuries and three surgeries.
Even though he felt his win owed something to Federer's off night, he didn't see why he couldn't press on in his bid to become the first Australian man to win a Grand Slam since Lleyton Hewitt at Wimbledon in 2002.
"Why not," he said of his chances of beating 13-time major winner Novak Djokovic in the quarterfinals.
"I'll have to improve a lot on the last time I played him," said Millman, who won just three games in a Queen's Club loss to Djokovic this year. "He's an incredible player and he's in really good form now, too.
"But why not? I think it's a disservice to who I am if I go out there and don't have that belief."