World number two Aryna Sabalenka got her clay court season underway with a straight sets victory on Wednesday over Barbora Krejcikova in the pair's fourth meeting of 2023.

Australian Open champion Sabalenka saw off her 12th-ranked Czech rival 6-2, 6-3 in just 75 minutes to become the first player into the quarter-finals.

Sabalenka, the runner-up in Stuttgart to Ashleigh Barty in 2021 and Iga Swiatek last year, had lost to Krejcikova in Dubai this season but gained revenge at Indian Wells and Miami.

Wednesday was their first career meeting on clay and Sabalenka was rarely threatened by the 2021 French Open champion.

"It's really difficult, but at the same time it helps me to learn how to stay focused from the first rounds and fight for every point," said Sabalenka on facing a fellow Grand Slam champion.

She hit 10 aces and never faced a break point as she cantered to her 21st win of the season, behind only Jessica Pegula and Elena Rybakina, who have each won 22 matches so far this year.

Wimbledon champion Rybakina reached that mark Wednesday with a 7-5, 6-3 win over Germany's Jule Niemeier.

Coco Gauff made her clay court season bow with a tough, mistake-ridden three-set win over Veronika Kudermetova.

The 19-year-old American, runner-up at the French Open last year, came through 6-2, 4-6, 7-6 (7/3) to set up a last-16 clash with another Russian player, Anastasia Potapova.

World number six Gauff committed 53 unforced errors with 24 winners, while Kudermetova hit 80 unforced errors to 35 winners. There were 15 breaks of serve in total.

"That was a close one," said Gauff. "I had opportunities in that match. I mean, again, I'm not expecting an easy match. She's been playing better and better each week.

"I think that I'm just going to have to keep that aggressive mindset, especially against her, someone who can come up with some big shots."

After easing through the first set, Gauff was 3-0 and 4-2 ahead in the second before 13th-ranked Kudermetova mounted a comeback.

In the decider, Gauff served for the match at 5-3. Kudermetova again hit back before the American prevailed in the tie-break.

Tunisian third seed Ons Jabeur made the quarter-finals for a second successive year by seeing off Jelena Ostapenko 1-6, 7-5, 6-3.

Top-ranked Swiatek starts her title defence on Thursday against highly-regarded Zheng Qinwen, the world number 25 from China.

Swiatek arrived in Germany having missed the Miami Open and Billie Jean King Cup qualifiers with a rib injury.

"I'm not injured anymore, so that's the most important thing for me," said reigning French and US Open champion Swiatek.