Debutant Dayana Yastremska knocked Donna Vekic out of the WTA Elite Trophy and Maria Sakkari was eliminated by Elise Mertens on Wednesday.

Yastremska, the youngest player in the tournament at the age of 19, won her Azalea Group opener 7-6 (8-6) 6-2 in Zhuhai.

The Ukrainian teenager unleashed a barrage of ferocious forehand winners in a high-quality contest, which proved to be Vekic's last of the season.

Rising star Yastremska rallied from 5-3 down in the tie-break after the pair could only force three break points between them in a serve-dominated first set.

Vekic did her best to withstand the force of the 10th seed in the second, but a fierce forehand winner put Yastremska a break up and a potent backhand return made it 5-2.

Yastremska served out the match and will face top seed Kiki Bertens for a place in the semi-finals.

Mertens earlier sent Sakkari out with a 6-2 3-6 6-1 victory in the Rose Group.

Sixth seed Mertens will face her doubles partner Aryna Sabalenka with a place in the last four on the line after beating Sakkari for the first time in five years.

Mertens won four games in a row in the final set to send Sakkari packing.

Sofia Kenin won the final match of the day, starting the tournament with a 6-4 6-4 success over fellow American Alison Riske.

Aryna Sabalenka reached the WTA Silicon Valley Classic final after easing past Donna Vekic on Saturday.

Belarusian Sabalenka – the second seed – was too good for Vekic, winning the semi-final 6-4 6-3 in San Jose.

Sabalenka and fifth seed Vekic traded breaks in the opening set but the former broke in the 10th game to close it out on her opponent's serve.

Vekic fended off a match point at 5-3 in the second set but it only delayed the inevitable as Sabalenka served it out in the next game.

Sabalenka – a three-time winner on the WTA Tour – will face Zheng Saisai in Sunday's decider.

Zheng stunned seventh seed and last year's runner-up Maria Sakkari 7-6 (7-5) 6-2 to advance to the final of the WTA Premier event.

After upstaging seeds Danielle Collins and Amanda Anisimova en route to the semis, Zheng continued her fine run as she eyes her maiden WTA crown.

Elina Svitolina was stunned by a Maria Sakkari comeback in the Silicon Valley Classic quarter-finals, while Aryna Sabalenka moved through on Friday.

Sakkari upset top seed Svitolina 1-6 7-6 (7-3) 6-3 at the WTA Premier event, saving four match points in San Jose.

The Greek seventh seed was trailing 5-2 in the second set before rallying for an incredible victory.

Sakkari will next face Zheng Saisai, who upset 17-year-old fourth seed Amanda Anisimova 5-7 7-5 6-4.

Zheng converted nine of 11 break points, including three from three in the final set, to battle through in two hours, 52 minutes.

Sabalenka and Donna Vekic, the second and fifth seeds respectively, moved into a semi-final clash.

While Vekic was too strong for qualifier Kristie Ahn 7-5 6-0, Sabalenka edged sixth seed Carla Suarez Navarro 3-6 6-2 6-4.

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