Serena Williams of the United States waves to the crowd as she leaves the court following her defeat in the women's singles match against Garbine Muguruza of Spain on day four of the French Open at Roland Garros on May 28, 2014 in Paris, France

Serena Williams of the United States waves to the crowd as she leaves the court following her defeat in the women’s singles match against Garbine Muguruza of Spain on day four of the French Open at Roland Garros on May 28, 2014 in Paris, France

*Defending French Open champion and world No. 1 Serena Williams was stunned by Spain’s Garbine Muguruza 6-2, 6-2 in the second round of the French Open today.

Muguruza, ranked No. 35, took only 64 minutes to secure her first ever victory against a top-eight opponent.

Garbine Muguruza of Spain shakes hands with Serena Williams of the United States at the net following her victory in their women's singles match on day four of the French Open at Roland Garros on May 28, 2014 in Paris, France

Garbine Muguruza of Spain shakes hands with Serena Williams of the United States at the net following her victory in their women’s singles match on day four of the French Open at Roland Garros on May 28, 2014 in Paris, France

SI.com reports:

Williams looked flat and never found her rhythm, finishing with 29 unforced errors and only eight winners while failing to win a point at net (0-for-5). The 17-time Grand Slam champion lost five consecutive games after holding to open the match. The 32-year-old American, known for her dominance on serve, was broken five times and won only 17-of-31 (55 percent) first-serve points.

“I don’t think anything worked for me,” Williams said. “It was one of those days. You can’t be on every day, and, gosh, I hate to be off during a Grand Slam. It happens.”

Muguruza, a 20-year-old Spaniard appearing in her second French Open, played lights-out tennis. She dictated most of the points and stayed aggressive. Muguruza hit 12 winners against 18 unforced errors.

In their only other meeting, Williams crushed Muguruza 6-2, 6-0 at the 2013 Australian Open. But since then Muguruza has climbed from No. 112 into the top 40. In January, she won the Hobart International as a qualifier for her first title, then reached the fourth round in Melbourne, the final of the Brasil Tennis Cup and the semifinals of the Grand Prix SAR.

Still, Muguruza entered the match as a heavy underdog, having gone 0-5 in her career against top-five players and 3-8 against the top 10. In her two most recent tournaments, she had lost to No. 19 Sam Stosur in the second round of the Madrid Open and to No. 61 Francesca Schiavone in the second round of the Italian Open. Williams won the latter event, dropping only one set in five matches.

“I have actually never seen her play like this,” Williams said. “Garbine played really well and she played really smart. I didn’t adapt.”

Venus Williams of the United States returns a shot during her women's singles match against Anna Schmiedlova of Slovakia on day four of the French Open at Roland Garros on May 28, 2014 in Paris, France

Venus Williams of the United States returns a shot during her women’s singles match against Anna Schmiedlova of Slovakia on day four of the French Open at Roland Garros on May 28, 2014 in Paris, France

Earlier Wednesday, Venus Williams lost to No. 56 Anna Schmiedlova 2-6, 6-3, 6-4. The Williams sisters would have met in the third round if both had won.