Canada's Bianca Andreescu has rallied to beat Garbine Muguruza of Spain 0-6, 7-6 (3), 6-1 in a clash of Grand Slam champions Sunday in the first round of the Adelaide International.

The 2019 US Open champion Andreescu trailed 0-6, 2-5 before staging a remarkable comeback to beat two-time major titlist Muguruza in 2 hours, 12 minutes. Andreescu improved her head-to-head record against former top-ranked Muguruza to 3-0.

"In the second set I really had to change my gameplan," 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."

Muguruza looked in outstanding form in the first set, hitting eight winners to two and converting three of five break points while not facing a break point herself.

Andreescu started the second set more strongly but Muguruza nailed a forehand winner to lead 4-2 and served for a 5-2 lead. Muguruza served for the match at 5-3 but Andreescu averted that danger and took a crucial 4-2 lead in the tiebreaker with a backhand down the line, before closing out the set with an ace.

Andreescu served well, then broke for 3-1 in the final set. She will now play either No.4 seed Veronika Kudermetova or Amanda Anisimova in the second round.