Down 4-2 in first set, Serena Williams rallies to reach U.S. Open semifinals

Serena Williams’ game still isn’t as precise as she’d like, but that’s to be expected for someone barely a year past childbirth and a terrifying array of complications. But her indomitable will is intact, and she summoned it at the right time Tuesday.

Down a break at 2-4 in the first set of her quarterfinal match against Karolina Pliskova, Williams had to take a stand or risk having to erase a huge deficit in punishing heat and humidity.

“I just wanted to play better at that point. I was playing really not a good game,” Williams said. “I felt like I just need to make less errors and see what happens.”

She won the next eight games, propelling her to a 6-4, 6-3 victory over seventh-seeded Pliskova and into a semifinal berth against Anastasija Sevastova, who upset defending champion Sloane Stephens 6-2, 6-3.

The triumph was Williams’ first over a top-10 player since she returned to competitive tennis in April.

“That’s a really big step for me. Shocking, my first top-10 win,” said Williams, who has six U.S. Open titles among her 23 Grand Slam singles championships.

“I really felt like I was playing well in Cincinnati, even though I lost,” she added, referring to her second-round loss in a pre-U.S. Open tournament.

“I was just on the verge. If I could have just had one more match before I played a top-10 player, I think I would have done better. I’m getting those matches now. Just was so light on the matches. So now I feel like I’m at a level where I can play and try to compete against these amazing women in the top 10.”

Pliskova, who defeated Williams in the quarterfinals here in 2016, said Williams was the better clutch player Tuesday. Pliskova also said she believes Williams can win the championship here.

“I feel like she has a big chance because the players which stayed, I feel like she can beat all them,” Pliskova said.

Williams isn’t thinking that far ahead, but she’s encouraged at her progress. She said before the tournament that she still had the fire to win, and that hasn’t changed.

“I don’t have 10 more years — at least I don’t think so. I said that 10 years ago,” said Williams, who will be 37 in three weeks. “I don’t think I have another 10 years of having opportunities to be able to play and win championships. Every match really means a lot to me. I kind of go out there and I just do the best that I can.”

Big win

In a battle of big-serving giants, No. 3 seed Juan Martin del Potro of Argentina defeated No. 11 John Isner, 6-7 (5), 6-3, 7-6 (4), 6-2, taking out the last remaining American man. Isner, who stands 6 feet10, committed 52 unforced errors to help 6-foot-6 del Potro reach the semifinals for the second straight year. Afterward, they shared a sweaty embrace at the net.

“He likes playing on a hard court like this. When he gets control of the point, it’s very tough to wrest it back from him,” Isner said. “He’s maybe playing some of the best tennis ever, for him.”

Del Potro, who won the Indian Wells title in March, triumphed here in 2009 before his career was interrupted by wrist injuries. Now healthy, he can choose between an effective slice backhand and two-handed backhand to supplement his formidable forehand.

“I’m very happy for my level, for what all has been through to get in this position now,” he said. “I think it doesn’t matter the final result in the tournament. I just enjoying playing tennis again. I’m enjoying a lot the crowds like this. I like to play big battles with other guys. That’s makes me feel alive again.”

Etc.

Jack Sock, Sam Querrey, Steve Johnson, Mike Bryan and Frances Tiafoe will represent the U.S in the Davis Cup semifinal against Croatia, to be played Sept. 14 in Zadar, Croatia. Marin Cilic, a quarterfinalist here, leads Croatia’s team. The U.S. hasn’t appeared in the Davis Cup Final since its 2007 triumph. This is the final year of the world group format before a World Cup format is adopted next year.

helene.elliott@latimes.com

Follow Helene Elliott on Twitter @helenenothelen