An error-prone Aryna Sabalenka overcame her early struggles on serve to overpower unseeded Belgian Maryna Zanevska 6-3 6-2 on Tuesday and move into the second round of the US Open.

Twice New York semifinalist Sabalenka, who is bidding to win her second Grand Slam title and leapfrog Iga Swiatek into top spot in the world rankings, was nowhere near her best but showed composure when it mattered most in a tricky contest.

The Australian Open champion made a shaky start with five double faults to drop serve twice, but Ukrainian-born Zanevska was unable to capitalise on both occasions to let her second-seeded opponent off the hook.

"First of all I want to thank you guys for staying because if I would be you, after the third double fault I'd leave the stadium. Thank you for being patient," Sabalenka, who made 23 unforced errors, told the crowd later.

"It was a tough start, it was so humid. I couldn't hold my racket. I'm glad I was able to get through this situation and get this win. She played an unbelievable match and she fought till the end. I'm just super happy with the win."

While Sabalenka continued to struggle for rhythm, there was no shortage of aggression in her groundstrokes as the Belarusian turned up the heat to claim four straight games for a 5-2 lead before closing out the opening set in 36 minutes.

The 30-year-old Zanevska, who announced her intention to retire after the tournament due to a chronic back issue, broke for the early lead in the second set but Sabalenka clawed her way back to 2-2 and never looked back.

Sabalenka broke again as Zanevska appeared to fade and finished off the match with two booming serves to book a meeting with Briton Jodie Burrage in the next round.

"I'm most pleased with my focus," said Sabalenka. "No matter what I was able to focus on myself and not on the score and just keep trying to find my rhythm. Hopefully I'll do better with every game."