VIENNA — American qualifier Frances Tiafoe rallied to beat Stefanos Tsitsipas 3-6, 6-3, 6-4 at the Erste Bank Open Thursday for his second win in four months over the top-seeded Greek.

Tiafoe upset Tsitsipas in straight sets in the opening round at Wimbledon in June, but failed to win a set when the pair met again at the Tokyo Olympics the following month.

However, the 49th-ranked American proved his triumph at the All England Club was no fluke, as he battled back from 3-0 down in the final set to win six of the next seven games.

Thursday’s win was Tiafoe’s first in seven matches against a top-three player, as Tsitsipas reached his career-high No. 3 ranking in August.

The result denied Tsitsipas a tour-leading 15th quarterfinal of the season.

In his fourth quarterfinal of the year, Tiafoe will take on Diego Schwartzman, who outlasted Gael Monfils 7-6 (5), 4-6, 6-2.

Second-seeded Alexander Zverev defeated Alex De Minaur 6-2, 3-6, 6-2 for the German’s 300th career win.

“This is definitely a massive milestone for me,” said Zverev, who next plays Felix Auger-Aliassime.

The sixth-seeded Canadian saved three match points before beating Britain’s Cameron Norrie 2-6, 7-6 (6), 6-4 in match between two contenders for the remaining tickets to the ATP Finals in Turin next month.

Jannik Sinner stretched his indoor winning streak to 10 matches and 20 sets by defeating Dennis Novak of Austria 6-4, 6-2. The seventh-ranked Italian will move into eighth position in the race for the finals if he beats Casper Ruud in Friday’s quarterfinal.

The fourth-seeded Norwegian edged last year’s finalist Lorenzo Sonego 7-6, 4-6, 6-4.