World number four Dominic Thiem of Austria missed a chance to reach a career-best third in the ATP rankings with a Rio Open quarter-final loss Saturday to Italy's Gianluca Mager.
Mager, a 128th-ranked qualifier playing in only his eighth career tour-level match, defeated 2017 Rio champion Thiem 7-6 (7/4), 7-5 in a match that was halted Friday by rain.
Had Thiem reached the semi-finals in his 2020 clay-court debut, he would have overtaken Roger Federer for third in Monday's ATP rankings.
Thiem was down a set and a break when rain stopped the match Friday with Mager leading 7-6 (7/4), 2-1.
Mager served for the match in the ninth game of the second set but Thiem broke to pull level at 5-5, only to have the Italian claim the final two games and the match after one hour and 55 minutes on the court.
Mager booked a semi-final date later Saturday against 106th-ranked Hungarian lucky loser Attila Balazs, who outlasted 133rd-ranked Spanish qualifier Pedro Martinez 2-6, 6-4, 6-2 in another rain-hit quarter-final.
Saturday's other semi-final pits Chilean third seed Cristian Garin and fifth-seeded Borna Coric of Croatia.
Austria's Dominic Thiem lost a rain-interrupted ATP Rio Open quarter-final match Saturday to Italy's Gianluca Mager