And now there are four.

With Madison Keys’ victory in the U.S. Open quarterfinals on Wednesday night, there are four American women in the semifinals of the home Grand Slam.

With her 6-3-6-3 win over Kaia Kanepi at Ashe Stadium, Keys booked her meeting with CoCo Vandeweghe Thursday night. Americans Venus Williams and Sloane Stephens face off in the other semi. It is the first time four Americans have occupied all four semifinal slots at the U.S. Open since 1981, when Tracy Austin, Chris Evert, Barbara Potter and Martina Navratilova achieved it.

“I was really nervous. I mean, on top of coming back after having a big win the other night, and then all of a sudden being in a match where you’re supposed to win, it was a lot,” Keys said.

“And then being the last American, it was really bad,” she said with a smile.

The last time four Americans were in any Grand Slam semifinal was 1985: Evert, Navratilova, Zina Garrison and Kathy Rinaldi.

With an all-American final assured, that will be the first since in the U.S. Open since 2002, and you might know the two combatants — Serena and Venus Williams. Serena was the winner.

advertisement | advertise on newsday

With highly effective first and second serves, Keys faced only three break points, all in the third game of the first set, and her serve got her out of that single spot of bother. She won 30 of 38 first serves, nine of 15 second serves.

Keys and Kanepi are two of several women’s comeback stories at this Open. Keys had left wrist surgery in November of last year, and had a second one after the French Open in June to remove scar tissue. She had returned in March of this year and victories had been hard to come by until she defeated Vandeweghe to win the Stanford tournament in July. She beat her again in the first round at Cincinnati in August.

“I’m going to have to serve really well,” Keys said of her match with Vandeweghe. “CoCo has an amazing serve. Defending that constantly, I’m just going to really have to do everything really well. The fact that we’re playing three times in a row is interesting.”

This was the fifth straight match that Keys played at night in the Open, including a third-rounder against Elena Vesnina that ended at 1:45 Sunday morning. Keys holds the record for the latest finish by a woman at the Open, playing until 1:48 a.m. last year in a win over Alison Riske.

Kanepi, 32, nearly quit the sport at the end of last year. She had plantar fasciitis in both feet and was suffering from Epstein-Barr virus, an autoimmune disease.

@NewsdaySports

The Estonian was once ranked 15th in the world in 2012 and had reached the quarterfinals of Grand Slams five previous times, the last one being Wimbledon in 2013.

She is ranked No. 418 and this is her first tour-level event of the year. She got into Open qualifying on a protected ranking of 196 and won three matches to reach the main draw. She got to the quarterfinals without having to beat a seeded player.

The two wrist surgeries cast a dark shadow on Keys’ career, one from which she has emerged full bore.

“I feel like wrist surgery is all the rage right now,” Keys said. “I feel like everyone is getting it done. There was definitely the fear that a lot of players have struggled coming back from it. Having to go in for a second one was obviously really scary. But my surgeon was amazing, and the whole time he told me I was going to be fine.”

Just not this fine.