She built a big lead then barely avoided getting pushed to a third set before beating 21st-seeded Naomi Osaka of Japan, 6-1, 7-6 (7), in a matchup of powerful baseliners.
Keys compiled a 30-8 edge in winners and started quickly, going up by a set and a break at 3-1 in the second. But she began making more and more mistakes, allowing Osaka to take 10 consecutive points and three games in a row during one stretch.
Still, Keys served for the victory at 5-4, and held a match point at 40-30, when she pushed a backhand long and wound up getting broken. In the tiebreaker, Osaka went ahead 4-1, and held set points at 6-5 and 7-6. Keys held steady, though, and was able to convert her second match point when Osaka double-faulted.
Second-seeded Alexander Zverev reached the fourth round for the first time, saving match point to win, 6-2, 3-6, 4-6, 7-6 (3), 7-5, against Damir Dzumhur, who collided with a ball boy in the fourth set.
Zverev struggled against the array of deft drop shots the Bosnian used to drag the German into the net, where he was less effective, after the first set.
Dzumhur, seeded 26th, had a match point on Zverev’s serve at 5-4 in the final set. Having never played a five-set match at Roland Garros until this year, Zverev has now won two back-to-back.