ACAPULCO, Mexico -- No.5 seed Sofia Kenin of the United States fought her way through a grueling barnburner to prevail over former World No.1 Victoria Azarenka of Belarus, 6-4, 4-6, 7-5, and reach the semifinals of the Abierto Mexicano TELCEL presentado por HSBC on Thursday night.

"Honestly, I’d just fight every point," Kenin said to the press, regarding her win. "[Azarenka is] not going to give up, and I knew I had to really just play my best in order to win. She’s a former No.1 player and Grand Slam champion with so much experience."

In the first meeting between the two players, World No.50 Azarenka was up early breaks in all three sets, and even served for the match at 5-4 in the decider, but Kenin was able to pull herself back level in each set, ultimately prevailing in the first and the final set to claim a hard-fought victory after two hours and 32 minutes of play.

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World No.35 Kenin had 12 double faults in the match, but fired 37 winners to Azarenka's 21. Each player had 13 break points, but Kenin converted eight to Azarenka's seven, the final one being on the last point of the match to seal her victory.

In the final four, Kenin, who won her first WTA singles title in Hobart in January, will face the winner of the nightcap quarterfinal between No.7 seed Zheng Saisai of China and Canadian teenager Bianca Andreescu.

"I played well, and the next match is going to be a tough one as well," said Kenin. "I’m just going to go out and play my best game."

Azarenka was doing well on serve initially, notching 10 straight points on her delivery to open the match. Combined with a break at 1-1, due to a Kenin double fault on break point, the Belarusian leapt out to a strong 4-2 lead.

But strong backhands by Kenin garnered her a crucial break to get back on serve at 4-4, as the American’s unforced errors diminished while her groundstroke speed picked up. Kenin held for 5-4 after starting that game with consecutive double faults, claiming her first lead since the first game and putting the pressure squarely on Azarenka.

A lengthy game ensued, with Azarenka holding two game points before Kenin reached set point twice. Azarenka staved them off and got back to game point, but big hitting by Kenin brought her a third chance, which she took with a wily angled backhand off a drop shot. Kenin out-winnered Azarenka in the set by 13 to 2.

Azarenka got off to an even larger early lead in the second set. Kenin struggled with double faults in the early stages of the set, and Azarenka twice found herself up a double break, at 3-0 and 4-1. But Kenin’s passing shots were on point, and she maneuvered her way back to parity at 4-4.

The American held two game points to take a 5-4 lead, but Azarenka ramped up her returning, reaching break point. There, a stunning volley completed Azarenka’s turnaround in that game, and she broke for 5-4. In the next game, an ace brought the Belarusian to set point, which she converted as a booming backhand caused an error from Kenin.

Azarenka started the decider with an early break, grabbing a 2-1 lead after a wide backhand miscue by Kenin. But the American quickly got back on serve at 3-3 after Azarenka misfired on groundstrokes of her own.

At 4-4, Kenin had two game points, which would have forced Azarenka to serve to stay in the match. But big hitting by the Belarusian pulled her back into that game, and she eventually clinched a service break, garnering a chance to serve for the match.

But with the win on her racket, Azarenka played a shocker of a game, dropping serve at love via an unforced error and two double faults, the second coming on break point. Back at 5-5, Kenin found new life, powering winners to hold for 6-5 and box Azarenka into a corner.

Serving to send the match into a tiebreak, Azarenka could not keep the American contained, and Kenin broke open a rally at 30-30 with a forehand winner to reach her first match point. There, another huge forehand by Kenin forced Azarenka to fire an error into the net, completing a steely comeback victory for the 20-year-old American.