Reilly Opelka hammered 24 aces and knocked off top-seeded Daniil Medvedev of Russia 7-6 (5), 7-6 (5) on Friday to advance to the Libema Open semifinals in ‘s-Hertogenbosch, Netherlands.

Medvedev built a 4-1 lead in the second-set tiebreak before self-destructing with three consecutive double faults to finish the one-hour, 36-minute match. Opelka will face unseeded Belgian Zizou Bergs, who held off Estonian Mark Lajal 7-6 (2), 7-6 (4).

The other grass-court semifinal pits No. 2 seed Ugo Humbert of France against Canada’s Gabriel Diallo. Humbert needed only 67 minutes to complete a 6-1, 6-4 win over Portugal’s Nuno Borges, while Diallo reached his second ATP Tour semifinal with a 7-6 (6), 6-4 upset of third-seeded Russian Karen Khachanov.

BOSS Open

Led by No. 1 Alexander Zverev, the top four seeds advanced to the semifinals with straight-sets wins in the quarterfinals in Stuttgart, Germany.

Home favorite Zverev saved both break points he faced in a 7-5, 6-4 win against Brandon Nakashima and moved on to face No. 3 seed Ben Shelton, a 6-4, 6-4 winner over Czech Jiri Lehecka. Shelton fired 18 aces and guaranteed a spot in the top 10 for the first time in Monday’s rankings with the victory.

Shelton’s fellow American, No. 2 Taylor Fritz, will meet No. 4 Felix Auger-Aliassime of Canada in the other semifinal. Fritz fired 12 aces in a 6-3, 6-4 victory over Hungary’s Marton Fucsovics, while Auger-Aliassime ended 17-year-old German Justin Engel’s memorable run with a 7-6 (3), 6-3 victory.

–Field Level Media