NEW YORK, NY, USA - No.21 seed Ekaterina Alexandrova roared through the final six games to defeat former World No.1 and three-time US Open champion Kim Clijsters, 3-6, 7-5, 6-1 and reach the second round.

"It was amazing," she said during her on-court interview. "She's a legend, and the fact that I beat her means so much for me. It's great experience and I'm just happy."

The Russian No.1 had her work cut out for her against an inspired Clijsters, who was five points from the first win of her latest comeback, to advance after an hour and 45 minutes on Court 17.

"She played extremely well, and I just told myself to play every point. It didn't matter if I was losing or winning: just stay focused on each point."

Clijsters came to New York as a wildcard aiming to play her first Grand Slam tournament since retiring for the second time at the 2012 US Open, having announced her comeback last fall and returned to action at the Dubai Duty Free Tennis Championships in February.

Initially among the Western & Southern Open wildcards, the Belgian opted to withdraw to maximize her chances of an official return to the USTA Billie Jean King National Tennis Center.

"I've been here for a while now without playing a match," Clijsters said in her post-match press conference. "That was a long, a long time to practice and be in the bubble for almost two weeks without playing a match. So I was excited to get out there and play my match. Obviously a late night tonight.

"But it's still fun to be out there. I enjoy it. My opponent is a great player. We had some good tennis out there. That's what it's all about, is trying to bring good tennis."

Alexandrova, who made her own Grand Slam main draw debut four years after Clijsters' 2012 retirement, began the year in fine form, winning her first career WTA title at the Shenzhen Open in January before making the Australian Open third round and her first Premier-level semifinal at the St. Petersburg Ladies Trophy.

Still it was Clijsters, still in search of a first win of the season, who enjoyed the quicker start, breaking the big-hitting Russian for a 3-1 lead and shook off losing a titanic eighth game to serve out the opening set at love.

Alexandrova responded well to break for a 2-0 lead of her own to start the second set. The former World No.1 quickly broke back and saved two set points in the all-important tenth game, the first with a scintillating lob. 

Undaunted, the No.21 seed saved a break point in the next game as she kept hopes of a deciding set alive.

Down a third set point, Clijsters unleashed a powerful forehand winner but couldn't force a tie-break as Alexandrova leveled the match.

"I felt like I had a couple chances early on in the second set where I had some break points," Clijsters said. "Kind of lost my footing a little bit where I had a shorter ball, missed it. Then she started serving a lot better, I felt. She started returning better. I was just missing less I think than in the first set.

"The third set, I felt like she was just seeing the ball very well, just hitting her targets all the time."

The Russian indeed saved her best for last, rallying from a break in the final set to win six straight games to clinch the clash in emphatic fashion.

"It's a process. That's what I told myself at the start when I took this challenge on, was that it's going to take a lot of hard work and losses. That's part of it.

"We'll see what's up next. To be honest, I'm not sure at the moment yet. We'll see. It's been a strange year, obviously. When I started in Dubai and Monterrey, I was excited to play more tournaments, have the family travel with me. But that obviously didn't happen. We'll see what the future holds."

In all, Alexandrova struck an impressive 29 winners to 32 unforced errors, while Clijsters made 22 winners to 36 unforced errors of her own. Breaking serve five times, the 25-year-old put down six aces and won 70% of points behind her first serve.

Up next for the No.21 seed is American Caty McNally, who dispatched Slovak star Viktoria Kuzmova in straight sets earlier in the evening.

2020 US Open highlights: Alexandrova quells Clijsters