BASEL, Switzerland (AP) — With Roger Federer getting an unexpected day off Friday, his next opponent Greece’s Stefanos Tsitsipas had to work hard to advance to the Swiss Indoors semifinals.

Third-seeded Tsitsipas rallied to beat Filip Krajinovic 3-6, 6-4, 6-4 in the quarterfinals, clinching when the 46th-ranked Serbian sent a service return long.

Tsitsipas was the main attraction Friday at Federer’s home town tournament after an all-Swiss quarterfinal became a walkover for Federer due to Stan Wawrinka withdrawing with a back injury.

Top-seeded Federer is seeking a 10th career title at Basel.

The other semifinal will pair unseeded Reilly Opelka and wild-card entry Alex de Minaur.

Big-serving Opelka sent down 31 aces in beating fourth-seeded Roberto Bautista Agut 6-3, 3-6, 6-3. The 37th-ranked American hit five of these aces consecutively to clinch the first set after trailing 0-40 with a 5-3 lead.

The 20-year-old de Minaur advanced past Jan-Lennard Struff 6-4, 7-6 (4).

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