American wildcard Amanda Anisimova claimed a sizeable scalp Monday in her return after eight months away from tennis, upsetting Anastasia Pavlyuchenkova in straight sets at the Auckland Classic.

Anisimova toppled her accomplished opponent 7-5, 6-4 in her first appearance on the WTA Tour since announcing in May she would take an indefinite break, citing burnout and concerns for her mental health.

The 22-year-old former French Open semi-finalist showed no sign of rust, displaying the powerful game that lifted her to a world ranking just outside the top 20 in her teens.

Anisimova spoke in the leadup to the tournament of being better equipped mentally for the rigours of the professional circuit thanks to her break.

She withdrew completely from tennis for four months, before gradually resuming training in September.

But she revealed she nearly didn't take the court for her first-round match after waking up with "horrible" muscle spasms in her shoulder.

"I was just so upset because I had the wildcard for this tournament," she said.

"I really wanted to play for myself today but also for the tournament -- I was really appreciative of them giving me the opportunity.

"Until the last second I wasn't sure so I'm proud of myself for coming out here and really pushing myself."

Anisimova also received treatment to her left upper leg after winning the first set, describing it as a "little tweak".

She emerged strongly, going 5-1 up in the second set against 32-year-old Pavlyuchenkova, a 12-time title winner and former French Open finalist.

Anisimova will play fifth seed Marie Bouzkova after the Czech beat Magdalena Frech 6-0, 3-6, 6-4.

The other seeds in action on day one were all victorious, namely third-seeded Ukranian Lesia Tsurenko, fourth-seeded American Emma Navarro and sixth seed Wang Xinyu of China.

Defending champion Coco Gauff will play her opening match on Tuesday, with the world number three and US Open title-holder having drawn American compatriot Claire Liu.