Zverev

TORONTO — Top-seeded Alexander Zverev of Germany led Francisco Cerundolo 6-4, 1-0 when the 14th-seeded Argentine retired because of an abdominal injury Saturday night in the National Bank Open.

Zverev advanced to face defending champion Alexei Popyrin of Australia in the quarterfinals. The 18th-seeded Popyrin beat fifth-seeded Holger Rune of Denmark 4-6, 6-2, 6-3 in the first night match.

Zverev, the 2017 champion ranked third in the world, ended up the top seed with top-ranked Jannik Sinner — the 2023 winner — and No. 2 Carlos Alcaraz skipping the hard-court event that ends Thursday. No. 5 Jack Draper and No. 6 Novak Djokovic also sat out.

Zverev won on clay in Munich in April for his 24th tour title.

Alex Michelsen reached the quarterfinals in the afternoon, topping fellow American Learner Tien 6-3, 6-3. Michelsen will face 11th-seeded Karen Khachanov of Russia, a 6-4, 7-5 winner over eighth-seeded Casper Ruud of Norway.