Fourth seed Aryna Sabalenka has beaten doubles partner and Belgian sixth seed Elise Mertens 6-4 3-6 7-5 to top their group and qualify for the semi-finals of the WTA Elite Trophy in China.

Despite making 10 double faults in the match, Belarusian Sabalenka — who has won three of her four singles titles in China — advanced after a physically taxing battle in two hours and 20 minutes in Zhuhai on Friday.

Sabalenka will play the Czech Republic’s Karolina Muchova, who fought long and hard for a second consecutive day and eventually came out on top with a 6-4 4-6 6-3 win over second seed Sofia Kenin to book her spot in the semis.

Muchova, who said she fought jet lag and a bout of dizziness in the second set, fired six aces and broke the American three times to win her second consecutive three-setter at the tournament.

China’s 12th seed Zheng Saisai lost 6-4 6-3 to Croatian fifth seed Petra Martic in their final round robin match but the local favourite still qualified for the semis.

With Zheng, Martic and Madison Keys winning one match each in their group, the Chinese 25-year-old needed to win at least seven games to advance if she were to end up losing the final match.

“This is the first time I’ve had this experience,” Zheng said.

“Actually, I knew if I win a set, I for sure would be in, but I don’t know exactly how many games.

“So I was pretty tight because I knew I don’t need to win the match. I was scared a little bit… very nervous. But she was pretty sure. She said, ‘congratulations’ and I was like, ‘Oh, okay, that’s great.'”

She plays top seed Kiki Bertens in the other semi-final after the Dutchwoman advanced on Thursday.