One destroyed racket — and one poor set — later, Serena Williams made it safely into the third round of the Rio Olympics as she bids for a second consecutive singles gold medal.

The No. 1-seeded American struggled for quite a while Monday night, before emerging with a 7-6 (5), 6-2 victory over France's Alize Cornet, despite making 36 unforced errors and getting broken four times.

"I just needed to relax. I was missing shots by, literally, centimeters, and I'm not really used to missing those shots," Williams said. "I really had to figure out a way to adjust."

Williams started well enough, taking the first three games and compiling 17 of the match's first 21 winners. But then she dropped 5 of 6 games to fall behind 5-4.

During that troublesome stretch, Williams reacted to losing two games in a row by mangling the tool of her trade, slamming it against the back of her green-and-white sideline bench before dismissively depositing it on the ground. Hardly the first time she's done that sort of thing — and likely not the last, either.

In her previous tournament, Wimbledon, Williams broke a racket after losing the opening set of a second-rounder against American Christina McHale. Williams then flung the racket so far behind her that it landed in the lap of a TV cameraman filming the match.

From that point on, Williams didn't drop a set the rest of the way at the All England Club, taking 12 in a row to earn her record-tying 22nd Grand Slam title.

She didn't quite generate that sort of spark Monday, 24 hours after she and older sister Venus lost an Olympic doubles match for the first time. They had been 15-0 with three golds, but that streak is now over.

So, too, is Cornet's three-match winning streak against the younger Williams.

That's because Williams cut down on her mistakes in the second set.

How?

"Just tried to add a little bit more spin," she explained. "If it's going out, maybe I'm hitting it a little bit too flat."

After three No. 1 seeds exited Sunday — Serbia's Novak Djokovic in men's singles, the Williams sisters in women's doubles, and France's Nicolas Mahut and Pierre-Hugues Herbert in men's doubles — Williams avoided that sort of result in singles.

Still, this was touch-and-go for more than an hour. Cornet held a pair of set points in the opener but failed to convert either. Then Williams served for that set at 6-5, only to get broken at love when she double-faulted for the fifth time. And in the tiebreaker, Cornet went ahead 5-4 before Williams claimed the next three points and the set.

She raced to a 3-0 edge in the second set, and that was pretty much that.

No tennis player ever has won two Olympic singles golds — let alone two in a row. But Williams is not just any player, of course. Which is why it was rather remarkable that Cornet, who is ranked only 48th and never made it past the fourth round of a major in 42 appearances, came into Monday with a 4-3 record against Williams.

"She knows how to play me. Every time I play her, I'm not in my best shape," Williams said. "I really wanted to be able to play well, because she always seems to play well."

Joining Williams in the third round: No. 2 Angelique Kerber of Germany, No. 3 Garbine Muguruza of Spain and No. 7 Madison Keys of the U.S.

Elsewhere, the man who got stuck in an elevator for 40 minutes and then beat Djokovic, Argentina's Juan Martin del Potro, got to the third round in men's singles but lost to Spain's Rafael Nadal in doubles.

Del Potro produced a 6-3, 1-6, 6-3 victory over Portugal's Joao Sousa, before heading back out on court with partner Maximo Gonzalez and getting beaten by Marc Lopez and Nadal 6-3, 5-7, 6-2.

In a tournament that began without half of the members of the ATP's top 10 — including Roger Federer and Stan Wawrinka — del Potro is suddenly looking like someone who might be able to add another medal to the bronze he took home from the 2012 London Olympics.

Because of injuries, del Potro had gone 2½ years without participating in a Grand Slam tournament until playing at Wimbledon, so one big question is what his fitness level is.

"I'm getting better. I'm in good shape, but I don't know if I'm prepared to play six or more matches," he said. "This week I'm just going slowly, trying to get better every day."