Andreescu, the 2019 US Open champion, trailed 0-6 2-5 before rallying to post a 0-6 7-6 (7-3) 6-1 victory.

Former world No.1 Murguruza, who won the 2016 French Open and the 2017 Wimbledon title, is winless against Andreescu in each of their three meetings.

Andreescu, 21, is looking to make an impact at this month’s Australian Open after skipping the tournament last year to focus on her mental health.

Now ranked world No.55, Muguruza looked in perilous form in the opening set, hitting eight winners to two.

She served for the match at 5-3 but Andreescu broke back and then levelled before taking a 4-2 lead in the tiebreaker and closing out the set with an ace.

Andreescu, ranked 46, said she knew mid-match she had to adapt or face an early exit.

“In the second set I really had to change my game plan,” Andreescu said.

“I told myself to go for it (and) whatever happens, happens.

“I put more returns in the court, more serves in the court. I’m so glad I pulled that out. I have no idea how.”

In the other matches on the opening day at Memorial Drive, Estonian veteran Kaia Kanepi also fought back to down Belarusian Aliaksandra Sasnovich 4-6 6-1 6-4.

Australian Storm Hunter lost in qualifying to Swiss Viktorija Golubic while compatriot Kimberly Birrell was no match for American Shelby Rogers.
-AAP