Francis Tiafoe literally grew up around tennis, often spending nights at a Maryland tennis center where his father worked. At only 16, he is ranked number two in the world. Could a future U.S. champion be in the making? (Lee Powell/The Washington Post)

In a 16-year career that has been interrupted by occasional bouts of illness and injury, Serena Williams has always competed with a ruthless intensity at Grand Slams, mindful that the majors ultimately define greatness in tennis.

That intensity deserted Williams on Saturday at Wimbledon, where the five-time champion and reigning world No. 1 was ousted in the third round by 24th-ranked Alize Cornet of France, who hit with more abandon and held her nerve for a 1-6, 6-3, 6-4 victory that represented her career highlight.

Not since 2005 had Williams, 32, been ousted so early at Wimbledon. It continued an uncharacteristic pattern, marking the third consecutive major in which Williams failed to reach the quarterfinals, following a second-round loss at the French Open and a fourth-round loss at the Australian Open.

“Right now, I don’t really know what I did wrong,” Williams said afterward, sounding utterly disconsolate and genuinely lost. “Usually I do. Usually I know I did this, this and that.”

With a hard-hitting, big-serving game that’s amplified on grass, Williams opened the tournament as the prohibitive favorite to win a sixth Wimbledon title, which would have tied her with Chris Evert and Martina Navratilova for second on the list of most women’s majors in the Open Era with 18. Steffi Graf retired with 22.

Reaching that mark of 18, Williams said, remains a career goal.

“It’s something I’m obviously going to keep going for,” said Williams, whose last major was the 2013 U.S. Open “It’s definitely something in my mind, pretty important.”

Given her inability to reach the final eight of the last three majors, it’s an open question whether something is amiss with Williams’s game or whether her rivals are closing the gap in terms of the power and competitive fire.

“I think in general everyone plays the match of their lives against me,” Williams said. “So I just have to always, every time I step on the court, be a hundred times better. If I’m not, then I’m in trouble.”

Cornet pumped both fists and looked to her guest box with disbelief upon clinching the victory, then crumpled to the ground to kiss the Court 1 grass.

It was one of just 11 matches completed on a rain-soaked Saturday.

Although Cornet had beaten Williams at a hard court tournament in Dubai in February, there was little reason to believe the Frenchwoman posed a threat to the No. 1 seed Saturday. Hardly a natural on grass, Cornet entered the match with a 6-7 record at Wimbledon, compared with Williams’s 72-9 mark.

While Williams insisted the defeat in Dubai had no bearing on Saturday’s outcome, it served as a template for Cornet, who studied videotape of the match to review the tactics that worked (her drop shot, in particular) and remind herself that the upset was possible.

“All these things helped me on the court to stay calm and know where I’m going,” Cornet said, “because otherwise Serena, she wouldn’t lose a single chance to make you feel that she is the boss on the court.”

Williams said she intended to go back and study the defeat to figure out where she’s falling short. For starters, her serve, regarded as the most feared weapon in women’s tennis, lacked its customary punch. In the 2-hour 4-minute match, she landed just three aces and committed seven double faults.

Williams also had as many unforced errors as winners (29), the most costly gaffes coming on her backhand side in the decisive third set.

But what stood out most was the caution with which Williams played when trailing in the third set.

Presented with opportunities to finish off points, she failed to go for the jugular. Twice in the third set she ran down drop shots only to shovel them over the net, keeping the ball in play rather than going for a winner.

After getting broken in the fifth game of the third set on a netted backhand, Williams looked despondent sitting in her chair at the changeover. And she proceeded to lose the next two games, giving Cornet a chance to serve for the match at 5-2 and again at 5-4.

“I know that I can do better,” Williams said. “I know that I have the potential to continue to be on top.”