Having never previously reached the second round at the French Open, two-time Grand Slam finalist Daniil Medvedev is now into the fourth round at Roland Garros.
The second-seeded Russian used 10 aces to beat No. 32 Reilly Opelka 6-4, 6-2, 6-4 and said the overcast conditions helped him to limit the big-serving American to five aces.
“The fact it was humid and wet helped me,” Medvedev said. “His serve was less fast.”
Medvedev has lost major finals at this year’s Australian Open and the 2019 US Open. He next faces No. 22 Cristian Garin of Chile.
Seeded fifth, Tsitsipas rallied to beat No. 31 John Isner 5-7, 6-3, 7-6 (3), 6-1 in a match that ended shortly before midnight. U.S. men went 0-4 on Friday, and Isner has now lost 13 consecutive matches when facing an opponent ranked in the top five.
Tsitsipas, a semifinalist last year, will next face No. 12 Pablo Carreno Busta.
Early in the afternoon, play was interrupted by rain on all courts besides the main stadium — where the roof was closed. Federico Delbonis said the interruption helped him calm down after stress started to get hold of him toward the end of the second set of his match with Fabio Fognini.
Delbonis took a quick shower and eventually prevailed 6-4, 6-1, 6-3 to reach the fourth round at a Grand Slam for the first time.
Fognini required treatment from a trainer after bloodying his hand by punching his racket strings in frustration multiple times early in the second set.
Following a marathon five-set battle, Alejandro Davidovich Fokina upset 15th-seeded Casper Ruud 7-6 (3), 2-6, 7-6 (6), 0-6, 7-5 in 4 hours, 35 minutes. In the final game that lasted 16 minutes, Davidovich Fokina hit an effective underhand serve to save a break point. Ruud appeared surprised by the serve and had to scramble to get in position for a backhand return that he netted.
Kei Nishikori followed up two consecutive five-setters with a one-set victory, reaching the second week at Roland Garros for the seventh time after qualifier Henri Laaksonen retired with a thigh injury while trailing 7-5.
Nishikori will next play sixth-seeded Alexander Zverev, who beat Laslo Djere of Serbia 6-2, 7-5, 6-2.
Information from The Associated Press was used in this report.