Aryna Sabalenka was swatted aside in straight sets by 34th-ranked Nikola Bartunkova in the third round of the China Open on Sunday, leaving the event without its top two seeds.

Czech player Bartunkova, 20, sent down four aces to beat the former world number one 6-4, 6-3 in one hour and 35 minutes.

“I focused on myself, to be calm,” Bartunkova said.

“She’s a legend… so I’m really happy that I won the match,” she said of the four-time Grand Slam champion.

Bartunkova next faces Austria’s Sinja Kraus in the round of 16.

Second-seeded Sabalenka squandered five chances to break serve in the sixth game of the first set, with Bartunkova strong on defence and firing deep.

The 28-year-old from Belarus threw on a cap for the eighth game of the first set as the women switched between playing in the shade and the sun, but it did not turn the tide in her favour.

A frustrated Sabalenka tossed her racquet at a break down in the fourth game of the second set, and lost on the first match point when she returned into the net.

Top seed Elena Rybakina — who weeks earlier replaced Sabalenka as World No. 1 — was ousted by Alina Charaeva in the second round on Saturday.

Top seed Alexander Zverev was scheduled to play Novak Djokovic later on Sunday in the quarterfinals of the men’s 500-level event also taking place.

The 39-year-old Serbian great enters the match with an extraordinary unbeaten streak in Beijing, but Zverev — last month’s US Open champion — is in the running for the top men’s ranking.