NEW YORK, NY, USA -- Alizé Cornet of France moved into her first-ever US Open round of 16 on Saturday night, as she led No.7 seed Madison Keys of the United States, 7-6(4), 3-2, on Arthur Ashe Stadium before the 2017 US Open finalist retired due to injury.

Cornet was forced to upend a poor head-to-head history to get a win over Keys, as the American had won all three of their previous meetings. However, the Frenchwoman edged Keys in a tight opening set, and the American started receiving upper-body treatment following the loss of that tiebreak. Five games passed in the second set before Keys felt too affected to continue.

World No.56 Cornet had reached the US Open third round four times previously, but was never able to break through that ceiling. Against Keys on Saturday night, though, Cornet made it through a clash which had no breaks of serve before Keys retired after 89 minutes of play.

"I'll try to enjoy the fact that I'm finally reaching the fourth round here," Cornet said, during her post-match press conference. "It's been something I've been looking for [since] I don't know when."

The critical first set was won by Cornet after saving a set point at 5-4, which was the only break point held by either player in the opening frame. Cornet kept her unforced error count low in the set, with only seven, compared to triple that number by hard-hitting Keys.

"I really want to enjoy the one and a half sets that I did really good," said Cornet. "Of course, I'm sad it ended this way, that Madison was in pain."

"About this first set, I'm really proud because I was fighting on every point," Cornet added. "Even when I was a set down, I stayed really focused, I stayed positive. I was really trying to apply the tactical plan that we set up."

"Madison is definitely playing super fast, like it's crazy the ball sometimes," the Frenchwoman continued. "In the second set I took a return, I couldn't even play the ball. Literally the ball came through me. It was definitely very important to be ready with my legs and to use these legs to bring the ball back as many times as possible."

In the fourth round, Cornet will face the surprise package of the tournament, unranked Tsvetana Pironkova, who is playing her first event in over three years. Pironkova has yet to drop a set this week, and earned her second successive Top 25 win over Donna Vekic on Saturday.

Pironkova leads the head-to-head with Cornet by 2-1, but they have not played each other since way back in 2011. The winner will advance to the US Open quarterfinals for the very first time -- and if Cornet can defeat Pironkova, it will be her first-ever Grand Slam quarterfinal showing in 57 main-draw appearances at majors.

"I've known [Pironkova] a long time, been playing together for years," said Cornet. "She's back like this, like nothing happened, and is playing the best tennis of her life. It's really impressive."

"I remember losing against her in the past, so I know she can play great tennis, especially amazing backhand," Cornet continued. "I might be the favorite for once tomorrow, like a real favorite. I don't care. It's going to be a good challenge anyway. We will see how it goes.

"I will talk with [coach] Sandra [Zaniewska] about the match tomorrow and how to approach this match the best way possible, because I've never made it to the quarterfinal in a slam. It's going to be definitely special for me to play on Monday. Maybe a little bit more pressure, but I'm ready for the challenge."

In the match, both players were getting through their service games with relative ease in the opening stages of the first set, as neither woman faced a break point through 4-4. After holding for 5-4, Keys had her chance to move to a commanding lead, earning the first break point of the day with a forehand down the line -- which also doubled as set point.

Cornet withstood that chance, pulling back to deuce after Keys fired a forehand miscue long, and the Frenchwoman pulled through the two-deuce game to a hold for 5-5. The big hitting by Keys and the grit and guile by Cornet kept the set at a stalemate, and the pair had to settle the issue with a tiebreak.

Keys started the breaker inauspiciously, with a double fault, and after Cornet used a backhand passing winner to reach 2-0, she seemed to be off like a flash. Keys found the range on her forehand to pull back to 4-3, but an overhead winner by Cornet on the next point let her reclaim the minibreak. Cornet eventually took the tiebreak 7-4 after consecutive wide service returns by Keys.

The trainer came out to work on Keys, apparently on her neck, directly following the breaker, and the American nearly jumped out to an early lead after the medical timeout. Keys, bolstered by beautiful backhands, held four break points in the opening game of the second set. Cornet, however, methodically hung tough and erased them all, helped along by some misfires on the return from Keys.

Another break point for Keys came and went at 1-1, and after Cornet routinely held serve for a 3-2 lead, the American retired, moving the Frenchwoman to a new milestone at the US Open.

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