Nice - Second-seeded John Isner of the United States beat Serbia's Dusan Lajovic 7-6 (3), 6-4 to reach the Open de Nice semi-finals on Thursday, while defending champion Ernests Gulbis lost 6-2, 6-4 against Austria's Dominic Thiem.
Isner, who had eight aces and saved both break points he faced, next plays Thiem, who broke the third-seeded Latvian's serve twice in each set in their quarter-finals.
Gulbis also double-faulted five times.
Meanwhile, 18-year-old Borna Coric of Croatia beat James Duckworth 6-3, 7-6 (3), breaking the Australian's serve five times, to set up a semi-final against fourth-seeded Leonardo Mayer.
Mayer was at his defensive best, saving all six break points he faced in a 6-3, 6-4 win against No. 8 Juan Monaco in an all-Argentine match.