Top seed and defending champion John Isner and his fellow American Ryan Harrison posted quarterfinal victories Friday at the Hall of Fame Tennis Championships.

The 6-foot-9 Isner smacked 12 aces in getting past South African qualifier Izak Van der Merwe 6-4, 7-6 (7-2) on the grass courts at the International Tennis Hall of Fame.

Isner beat diminutive Belgian Olivier Rochus in last year's Newport finale.

The towering Isner will meet the sixth-seeded Harrison in a semifinal here on Saturday, the same day the Tennis Hall of Fame will induct its Class of 2012, including former players Jennifer Capriati, Gustavo Kuerten and Manuel Orantes.

The rising 20-year-old Harrison was leading Benjamin Becker 6-4, 3-0 when the German qualifier retired on Day 5.

Saturday's other semi will pit Aussie Lleyton Hewitt against American Rajeev Ram, who was a surprise champion here three years ago. The long-time ATP star Hewitt is a former world No. 1 and two-time major titlist.