Playing Grand Slam tennis for the first time since fracturing his right knee last year, the ninth-ranked del Potro is into the second round of Roland Garros and savoring each step.
His 3-6, 6-2, 6-1, 6-4 first-round victory over Nicolas Jarry neatly summed up how del Potro turned the match around. On a chilly Tuesday morning on Court Suzanne Lenglen, against a player he'd never met before, del Potro started poorly. He was broken in his first service game when Jarry ended a 14-shot rally with a forehand volley at the net.
But after losing the first set, Del Potro started to figure out his 58th-ranked opponent from Chile and took control. He saved a break point in the second set and another in the fourth before serving out the win, seemingly untroubled by his knee on the red clay.
A semifinalist at Roland Garros last year, del Potro said he wants to reach the point where his knee, and other injuries that have plagued the 30-year-old Argentine's career, are no longer lurking in the back of his mind. The injury forced him to miss this year's Australian Open, a comedown after his run to the final of last year's US Open, which he lost to Novak Djokovic.
"My main goal is still the knee, my health. And I'm looking forward to be 100% in the second part of the year,'' del Potro said. "Once I get in good shape again, I can be focused on the result, you know, in different tournaments, different surface. That's what I want to think about it, not only my knee or my wrist or whatever.''
A semifinalist in Paris in 2009, del Potro missed the French Open in 2010, 2014 and 2015 with left and right wrist injuries and in 2013 because of a respiratory illness. Seeded eighth this year, del Potro will next play Yoshihito Nishioka of Japan, ranked No. 72.
Zverev struggled in breezy and occasionally drizzly conditions. A year ago in Paris, the German needed to win three consecutive matches that went the full five sets to get to his first Grand Slam quarterfinal.
He was shaky in the middle of the match against Millman, who upset Roger Federer at the 2018 US Open.
No. 42-ranked Taylor Fritz, 21, defeated Australia's Bernard Tomic 6-1, 6-4, 6-1 for a career first in the Roland Garros main draw. He was also the first U.S. man to win and will next face Spain's Roberto Bautista Agut, the 18th seed.
The Associated Press and ESPN's Bonnie Ford contributed to this story.