SAN JOSE, CA, USA - In marathon fashion, Zheng Saiai advanced to the semifinals under the lights at the Mubadala Silicon Valley Classic.

In a marathon match that lasted two hours and 52 minutes, the World No.55 outlasted the American teenager, 5-7, 7-5, 6-4 to reach the biggest semifinal of her career to date.

"It was such a battle today. You never know until the end who's going to win. The third set in the end, a few points decided who was the winner. I'm really happy I got through this," Zheng said on-court after the match.

"I played her last time and I knew she has unbelievable talent. She has great touch and really aggressive game, and it was going to be tough anyway. I just gave my all. I just tried to hit it back and when I had a short ball, I go and try to enjoy."

Last fall, the pair met in the quarterfinals of the Hana-cupid Japan Women's Open, and the American dropped just two games en route to a 6-1, 6-1 victory - at the event where she reached her first WTA final - but the match couldn't have been more different with a Premier-level semifinal at stake.

Anisimova racked up 54 unforced errors over the course of the match, as the American struggled both physically with her own body, being seen by the medical staff in between the second and third sets, and the dogged defenses of the Chinese No.3.

The No.4 seed's error count doubled her winner total, which stood at 27, as the match saw a combined 17 service breaks.

Though both players had ample opportunities in the match, it was Zheng who proved the more effective: the World No.55 won nine of the 11 break point chances she created, while Anisimova went just 8-for-16.

The American trailed 3-1 in the opening set only to turn it around and lead 5-3, but saw two set points slip by on serve in the ninth game before she eventually broke Zheng for a third time - at love, to boot - to seal the lead.

The pair later traded breaks three times in the second set, with the Chinese playing striking first before Anisimova hit back each time.

Though she proved unable to send the match to a decider the first time she served for the second set at 5-4, Zheng made no mistake the second time, as she erased a break point and pushed the match the distance. 

In the final set, Zheng again was the first to lead, as she led by a break twice after the first three games, and though she was broken once more in the eighth game for 4-4, she held her nerve, and serve in the end, erasing two more break points in the final game.

Zheng will next face No.7 seed and 2018 finalist Maria Sakkari for a spot in the final, as the Greek No.1 pulled off an incredible win of her own to beat top seed Elina Svitolina in the quarterfinals.