BRISBANE, Australia - US Open champion and No.2 seed Naomi Osaka became the first player through to the quarterfinals at the Brisbane International on Tuesday as she defeated Australian teenager Destanee Aiava, 6-3, 6-2.

Never losing serve over one hour and eight minutes, Osaka saved all six break points she faced, served nine aces, and broke the qualifier's serve three times.

"I didn't really serve that much during off-season, because I hurt my shoulder a little bit," Osaka told reporters. "So honestly, I was just really glad that I could serve well today. But I think one of the things that I was working on more is like trusting my fitness level. And even though it didn't seem like it because I was blasting half of the balls, I was trying to construct the point a little bit, so I think that's what mattered to me the most."

Early breaks in each set helped set the tone for Osaka's victory, as she held serve from 0-40 in the third game of the opener before winning her first game on the teenager's serve immediately after. 

The Japanese No.1 served seven of her nine aces for the match in the opening set and didn't face a break point after taking the lead, though she ultimately needed four set points to seal an early advantage. 

In the second set, Osaka won five straight games after Aiava held serve to begin, saving a break point in the sixth game and two in the final game of the match to become the first player through to the last eight.

The US Open champion is making her main draw debut in Brisbane this week, having fallen in qualifying of the Premier-level event in her last appearance at the tournament in 2016.

"It's always great to start with a win," Osaka said. "I was really nervous coming out here because I felt like this is one of the matches I'm expected to win. But playing against someone like her who's a bit unpredictable and very strong, it was like one of those moments where I felt like I just have to stay really calm, but I couldn't. So I'm just really happy that I could play well."

Up next, the World No.5 will face either No.8 seed Anastasija Sevastova, who defeated another Australian in Daria Gavrilova on Tuesday in straight sets, or British qualifier Harriet Dart.