Serena Williams turns 35 later this month and once again appears invincible as she approaches her U.S. Open quarterfinal against Simona Halep on Wednesday.

So, might she be able to keep this up this level of play until age . . . 40?

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“No, no, no,” six-time Open champ Chris Evert told Newsday during a break in analyzing the tournament for ESPN last week. “She cannot keep it up until she’s 40, because this is a woman who is not going to keep playing if she’s [ranked] No. 20. If she’s No. 2 that will be OK, because that’s a challenge for her.

“Right now it’s more about health and injuries with her rather than technique and strategy. It’s really keeping her body healthy. Serena healthy, with her A game, is better than anybody - right now. But it has been a struggle this year for her. She could lose the No. 1 ranking.

“She’s only played seven tournaments [that count in the rankings] and she needs to get to the semifinals or else she’s not going to be No. 1.”