RIYADH, Saudi Arabia — Top-ranked Aryna Sabalenka eased to a straight-set victory over Zheng Qinwen in the opening match of the WTA Finals in Saudi Arabia on Saturday.

Sabalenka won 6-3, 6-4 to extend her perfect record against the Chinese player to 5-0. It was also her 21st win in her last 22 matches.

The seventh-seeded Zheng lost the last three games as her focus slipped, and also appeared to have lost track of the score. After hitting a backhand long on match point, Zheng headed toward her chair on what she seemed to think was a change of ends instead of going to the net for the traditional handshake.

She smiled and held up her hand in apology after realizing before heading back to the center.

The victory also sets up Sabalenka for ending the year at the top. The Belarusian player only needs to win two of her three group matches to ensure she retains the No. 1 ranking.

Fourth-seeded Jasmine Paolini of Italy beat fifth-seeded Elena Rybakina in the other Purple Group match.

Paolini, who is enjoying a breakout season, edged a tight match 7-6 (5), 6-4 on her debut at the year-ending tournament for the top eight ranked players.

American players Coco Gauff and Jessica Pegula will face off in the Orange Group on Sunday after second-seeded Iga Swiatek takes on Barbora Krejcikova.