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."