Australia, Jan. 21 -- Even as his uninterrupted dominance of yore dissipated, even as he took the occasional break, Roger Federer always mattered more often than not in the closing days of Grand Slam tournaments.

Until lately, that is.

Until, at age 37, he was outplayed in the Australian Open's fourth round by a much younger man, 20-year-old Stefanos Tsitsipas, during a 6-7 (11), 7-6 (3), 7-5, 7-6 (5) surprise that ended Federer's bid for a third consecutive championship at Melbourne Park.

"I have massive regrets," said Federer, who failed to convert any of the 12 break points he earned against Tsitsipas, the first player from Greece to reach a major quarterfinal.

This loss makes it a fourth straight Slam without Federer in the semifi...