World number one Victoria Azarenka moved into the quarter-finals of the Brisbane International with a hard-fought 6-3, 6-3 win over German Sabine Lisicki on Wednesday. Azarenka was made to work hard for her win by the hard-hitting Lisicki, who traded punishing ground strokes with the top seed but was let down by a high error rate -- 36 unforced errors compared with only nine from her opponent.

In a match much closer than the score suggests, Lisicki had her chances but was unable to take them. She had eight break points on Azarenka's serve but was only able to convert three, whereas Azarenka -- who won her maiden WTA title in Brisbane in 2009 -- broke Lisicki six times to seize the advantage.

The German also served poorly, landing only 52 per cent of her first serves and sending down five double faults. But she stayed in the match thanks to the quality of her hitting from the baseline. "I knew what kind of player she is and I felt like she did improve from maybe the last time we played," Azarenka said.

"I just knew that there is something that I have to deal with. So I was prepared to take some bullets today. But I just tried to stay focused on executing my game. I knew she was going to make some, she was going to miss some, so I just had to stay with her and look for my chance."

Azarenka now plays Kazakhstan qualifier Ksenia Pervak in the quarter-finals. Earlier, Germany's Angelique Kerber, the only player to defeat Serena Williams since the French Open in May, came from behind to beat unheralded Puerto Rican Monica Puig in three sets.

The 24-year-old fourth-seed looked in huge trouble as she trailed 1-4 in the third set but fought back to force a tiebreak. Puig then led 4-0 in the tiebreak only for Kerber to fight back again and take the match 3-6, 6-4, 7-6 (9/7) in two and a half hours.

She will next take on Russia's Anastasia Pavlyuchenkova in the quarter-finals. "I was just thinking point by point (when she was down in the third set)," Kerber said. "I was not thinking 'What's happening?' I was just really on court and just trying to hit the ball, move very well, and just fight for every point. It was a surprise how she played. I didn't know her before, but I'm sure that she'll top 50 soon."

Sloane Stephens set up a quarter-final against fellow American Serena Williams when she beat Sweden's Sofia Arvidsson 6-3, 6-4. Ukraine's Lesia Tsurenko, who only came into the tournament when Maria Sharapova pulled out, downed Australia's Jarmila Gajdosova 1-6, 6-1, 6-4.