Belinda Bencic of Switzerland (Clive Brunskill/Getty Images)

At the height of her powers, Serena Williams strode into Grand Slam tournaments with a two-fold advantage before a single ball was struck. Few women could match the power of her groundstrokes; fewer still could match the force of her will.

But this season, the world No. 1 has lost that aura of invincibility. After failing to reach the quarterfinals of a third consecutive major, Williams conceded here at Wimbledon that something was amiss in her game. And Tuesday, she was forced to retire from her doubles match after an illness left her too light-headed and disoriented to land a serve.

Meanwhile, a new generation of challengers isn’t waiting to figure out what ails the 17-time Grand Slam champion. Led by 20-year-old Eugenie Bouchard of Canada, these upstarts have closed the gap in terms of power and will-to-win.

“I believe in myself,” Bouchard declared after storming into Wimbledon’s quarterfinals earlier this week. “Every match I play, I believe I can win.”

Along with Spain’s Garbine Muguruza, who ousted Williams in the second round of the French Open, American Madison Keys, who won her first WTA tournament last month in Eastbourne, and a host of others, these teens and young 20-somethings have injected a dose of uncertainty into the women’s game.

Billie Jean King, who founded the Women’s Tennis Association 41 years ago, couldn’t be more thrilled.

“This is the most exciting time in women’s tennis that I can remember,” said King, noting that at 70 she has considerable perspective on the issue. “It’s really exciting around Wimbledon this year compared to the last few years. Anything can happen. All these young kids are starting to really come through now. There’s a buzz this year — a vibe around the grounds that we’ve not had for a while.”

Hall of Famer Chris Evert, now a commentator for ESPN, sees the same headline at Wimbledon.

“It’s the newcomers. The young guns,” Evert said, reeling off a list that includes Pittsburgh’s Alison Riske, 23; Cleveland’s Lauren Davis, 20; Chicago’s Taylor Townsend, 18; Switzerland’s Belinda Bencic, the 2013 Junior French and Wimbledon champion; Bouchard and Muguruza, before noting that she could keep going.

“They’re not up-and-coming; they’ve arrived,” Evert said. “This new group is fearless and confident and believes, ‘We’re ready to take over.’ They all feel like they want to take over.”

Bouchard makes no bones about it with her aggressive tactics, pouncing on the ball early, before her opponent can get set, and exploiting every opportunity to ratchet up the pressure. That’s what she did in her fourth-round match against Alize Cornet of France.

Bouchard’s path to Saturday’s championship got a bit easier Tuesday with the ouster of Maria Sharapova, the favorite to claim a second Wimbledon in the wake of Williams’ early defeat.

Bouchard, whose mother named all three of her children after members of Britain’s Royal Family (Eugenie, Charlotte and Williams) walked out to Wimbledon’s Center Court as if it were her birthright. She was the aggressor at the outset and dug in with even more tenacity in the first-set tiebreak and after falling behind, 2-4, in the second set.

Her grit won plaudits from nine-time Wimbledon champion Martina Navratilova, who is providing commentary for the BBC. “If she stays healthy, the sky’s the limit,” Navratilova said of Bouchard, the only woman to reach the quarterfinals of all the majors this season.

None of this is to suggest that Williams won’t win another major. After leaving Wimbledon’s grounds Tuesday afternoon, Williams issued a statement attributing her debilitating illness to nothing more than a “bug.”

Assuming it’s merely that, Williams may well have another Grand Slam title in her — if not multiple. With one more, she’d tie the mark of 18 shared by Evert and Navratilova.

For much of her time atop the world rankings, Williams had little trouble fending off her peers for major titles, whether Ana Ivanovic, Svetlana Kuznetsova, Justine Henin, Lindsay Davenport, Dinara Safina or Sharapova.

But Williams will turn 33 in September. And there comes a point in all professional athletes’ careers when no amount of training, ambition or anger can produce the same results. There comes a point when they start piling up losses to players who never posed a particular threat before.

The sport’s new generation didn’t grow up with Williams, like the 30-somethings who compiled records of futility against her. And that leaves them blissfully unburdened, in the view of analyst Mary Carillo.

“I’m not sure that these young kids have to deal with that — the history of Serena, the force of her, how intimidating and powerful her game is,” Carillo said. “That, to me, is a psychological difference. These kids hit hard They feel like they have a chance. She’s having a tough season, there’s no two ways about it. And these kids are paying attention.”

Britain’s No. 1 Heather Watson, 22, backs that theory up.

“Whether it’s a top 10 or top 20 player, these younger players all believe they can win,” said Watson, currently 60th in the world. “That’s what is so dangerous at the moment, because you see Serena getting knocked out in the early stages of Grand Slams now. I feel like this new generation is just so confident and feels they can beat anybody.”