Nice, France (SportsNetwork.com) - Second seed John Isner secured a berth in the semifinals, while defending champion Ernests Gulbis was sent packing Thursday at the Nice Open, a final clay-court French Open tune-up.

The 6-foot-10 American Isner topped Serb Dusan Lajovic 7-6 (7-3), 6-4, while Austrian Dominic Thiem doused the third-seeded Latvian Gulbis 6-2, 6-4 on the red clay at Nice Lawn Tennis Club.

The world No. 25 Gulbis has won only two matches this year, going a dismal 2-12. He beat Argentine Federico Delbonis in last year's Nice finale.

Isner will face Thiem in Friday's semifinals.

"I thought it was a pretty high quality match," Isner said after defeating Lajovic. "I played pretty well. As it is in a lot of my matches, it came down to a few points in the first and second sets."

The other semi will pit fourth-seeded Argentine Leonardo Mayer against rising young Croat Borna Coric. Mayer handled eighth-seeded fellow countryman Juan Monaco 6-3, 6-4, while the 18-year-old Coric beat Aussie James Duckworth 6-3, 7-6 (7-3) on Day 5.