#Serena Williams has ‘a lot of question marks’ at US Open

Serena Williams used to turn it on most when the pressure was at its peak — deep in Grand Slam tournaments.

That hasn’t been the case of late for Williams, stuck on 23 Grand Slam titles since she won the Australian Open in January 2017. Granted, she had a year-plus absence while having a child, but that drought has included two bitter defeats in U.S. Open finals.

At 38, Williams still remains one major away from tying Margaret Court — and it could well be a mental block.

“I’ve been definitely proudly stuck here, party of one,’’ Williams said sarcastically. “I’m pretty happy about it.”

“I’m never satisfied,” added Williams, who opens Tuesday against American Kristie Ahn. “That’s been the story of my career. It’s like I’ll never be satisfied until I retire. I’m never going to stop until I retire. It’s just my personality.”

She’ll be the fan favorite at the Open, which begins Monday and has no live fans — except for some of the players.

“I consider her the greatest tennis player of all time,’’ said 16-year-old sensation Coco Gauff, who opens Monday against Anastasija Sevastova. “Regardless I’ll look at her that way whether she gets 24 or not. When I watch her play, I normally am rooting for her.”

In the two tune-ups, Williams lost early.

“She still a lot of question marks,’’ ESPN’s Pam Shriver told The Post. “Five or six times, she’s losing a lot of close ones when she has a chance to put it away and that plays on her mind. That’s a reversal from her career.”

Last year’s bid was ended by Canadian upstart Bianca Andreescu, who opted out this year because of COVID-19 concerns.

Andreescu’s friend and former WTA player Julia Elbaba said Andreescu didn’t get in enough proper training.

“Bianca’s first priority is always taking care of her injuries as she knows the repercussions when they don’t listen to their bodies’ needs,’’ Elbaba told The Post. “Unfortunately with COVID, players like Bianca haven’t been able to train both mentally and physically in 2020 as much as they would’ve liked or needed to.”

It still leaves the women’s draw a lot more fascinating than the men’s side missing stars Roger Federer and Rafael Nadal.

Old friend Kim Clijsters is making a comeback at age 37. The Belgian is a three-time Open champion but hasn’t played singles here since 2012. She emerged in July in the World Team Tennis season held in a bubble in West Virginia.

Though she eventually pulled her abdomen, she earned an Open wild card. Last year she was inducted into the Open’s Court of Champions.

“My stomach is feeling much better,’’ said Clijsters, who lives part-time in New Jersey with her husband, former Villanova basketball standout Brian Lynch, and their three children. “I felt in World Team Tennis, my level really went up to where I want it to be. I felt like I played some really good tennis there. Hopefully I can kind of drag that through here. I’m hitting the ball clean. I’m starting to read my opponents better. That was something that I was missing in the first couple tournaments I played, is anticipation.’’

The fan-less Open has Clijsters intrigued — happy to roam the grounds freely and watch other matches.

“Walking around the courts, I’ve never been able to watch so many live tennis matches as in the last week at the site here [at the Western & Southern Open],’’ Clijsters said. “There’s always room to sit down. I just enjoy watching tennis. I enjoy the sport. Yeah, I mean, there was no reason. Obviously it’s fun when you get to go to a stadium and watch Serena play, you get to go to a stadium and it’s empty and Novak Djokovic is playing.’’