Former Australian Open champion Naomi Osaka has survived an early scare against unheralded Brit Katie Boulter to book a quarter-final berth in a Melbourne Summer Series event.

World No.3 Osaka, who won the Melbourne Park major in 2019, was made to work for a 3-6 6-3 6-1 victory.

Osaka was forced to step up her game after a low-key start but showed her championship qualities with some heavy ground strokes and damaging serving proving decisive.

Boulter, who is ranked 371st but playing on a protected ranking due to a run of injuries, impressed but couldn’t go with the US Open champion in the deciding set.

“After I lost the first set I just thought, I just want to fight as hard as I can,” Osaka said.

“She was playing really amazing so I thought if I lose it’s OK but I have to give my best effort.”

The 23-year-old superstar said she didn’t mind playing a longer match as she continues to build toward next week’s Open, after only conceding four games in her second-round encounter.

“Honestly I like playing long matches, just because I can gauge the condition of the court and I feel my fitness gets better,” Osaka said.

“I played a shorter match yesterday so maybe subconsciously I made myself play a long match today.”