CoCo Vandeweghe hasn’t won a tournament this year, but she’s having one Grand Slam of a season.

A semifinal finish at the Australian Open, a quarterfinal finish at Wimbledon, and now she’s through to the fourth round of the U.S. Open. A ruggedly fashioned 7-5, 4-6, 6-4 victory over wily veteran Agnieszka Radwanska at Arthur Ashe Stadium on Saturday put her in territory she’s never been before in her home Grand Slam.

The granddaughter of former Knick Ernie Vandeweghe and the niece of former NBA player Kiki Vandeweghe was born in New York and spent some of her early childhood in Locust Valley before moving to California. The 25-year-old has taken some time to climb the ladder from 2008 when she was the Open’s girls champion at age 16.

“I was definitely expecting a way different kind of professional career at the get-go,” Vandeweghe said. “Unfortunately, it was not to be, with injuries, learning curve, and also a learning curve of what the professional tour is. I was 16, still growing, still maturing. It took some time for me. I was a very immature 16-year-old as far as development-wise. I think I took some lumps definitely to get to where I am now.”

Radwanska has played in the upper echelons for a decade. Since her debut in the Slams at Wimbledon in 2006, she has played 46 consecutive majors. She’s never won one, but she has a slew of semifinals and 20 career titles. She is a deliberate, point-building player, a wall that is difficult to penetrate. She must hold the patent on patience in Poland, and it was testimony to Vandeweghe’s maturity that she won 21 points to Radwanska’s 16 on rallies of nine-plus shots. It took 2 hours, 56 minutes for the win, so patience was part of Vandeweghe’s repertoire, as well.

“I decided today, you know, I was going to hold strong in the rallies, fight for the long games was a big focus of mine, compete really hard,” Vandeweghe said. “I was making a lot of long service games for her. I think that eventually started to wear into her service games the longer and longer the match went on.”

Vandeweghe is part of a pretty good movement by American women players at the Open. Jennifer Brady, 22, who has never won a tour level tournament and is ranked 91st, took out Monica Niculescu, 6-3, 4-6, 7-6 (3), to make it to the fourth round of a Slam for the second time this year, after having made it at the Australian Open at the start of the season. She was a qualifier there.

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“If somebody told me that, I probably would not have believed them,” said Brady, who has done a lot of kicking around on the lower circuits. “I’m just kind of taking it all in and enjoying the moment.”

American Shelby Rogers got a good test but ultimately lost to the Open’s fourth seed, Elina Svitolina, 6-4, 7-5.

No. 15 seed Madison Keys beat No. 17 Elena Vesnina, 2-6, 6-4, 6-1, in a match that began shortly before midnight and ended at 1:45 a.m. Sunday. With Venus Williams and Sloane Stephens playing Sunday in fourth-round matches, five Americans will play in the round of 16.

When that fact was presented to Vandeweghe in her on-court interview, she replied: “It’s not about us. It’s about you guys here at the U.S. Open, cheering us on and pushing us through.”