Two-time Australian Open champion Azarenka found herself in trouble trailing 5-1 but she summoned up her fighting spirit to save five set points before edging a tense tiebreaker.

The Belarusian secured an early break in the second set, but surrendered the advantage before winning another tiebreaker against her Ukrainian opponent to wrap up victory on her fifth match point and set up a meeting with China's Zheng Qinwen.

"When you talk about first matches that are never easy this one was definitely at the top of the list," Azarenka said. "I played an opponent who played really, really well today.

"She already had two matches under her belt so she had a bit of momentum, especially at the beginning of the match.

"I couldn't find my footing and to transfer everything I'd been working on in the off-season in the match, it's step by step and I hope to do a little bit better tomorrow."

WTA Newcomer of the Year in 2022, Zheng saved a match point to battle past Anett Kontaveit 6-1 4-6 7-6(7), while former French Open runner-up Marketa Vondrousova upset eighth seed Ekaterina Alexandrova 4-6 6-3 6-2.

Former French Open champion Jelena Ostapenko later defeated former world number one Karolina Pliskova 6-1 6-3 to reach the second round.

RADUCANU WINS IN AUCKLAND

Returning to action following a wrist injury, former U.S. Open champion Emma Raducanu (20) dropped the first set in a rain-hit clash with Linda Fruhvirtova in her Auckland Classic WTA 250 opener before beating the Czech teenager 4-6 6-4 6-2.

"What a battle," Raducanu said of the clash with her 17-year-old opponent. "Linda is such a great young player and it was a different dynamic for me because normally I am the younger one."

Top-seeded American Coco Gauff made short work of Tatjana Maria, beating the Wimbledon semi-finalist 6-4 6-1 to snap a five-match losing streak.

Former US Open champion Sloane Stephens' match against Rebeka Masarova was suspended due to showers before being moved to Wednesday.