MELBOURNE — Title favorite Serena Williams and defending champion Victoria Azarenka advanced in contrasting styles Saturday to the fourth round of the Australian Open.
Williams, aiming for a third consecutive major title, recovered from a break down in the second set to win six straight games and finish off a 6-1, 6-3 win over Japan’s Ayumi Morita in 66 minutes.
The 15-time major winner even surprised herself with another serve at 128 miles per hour, matching her career fastest serve hit earlier in the tournament.
Top-ranked Azarenka struggled to hold off injured American Jamie Hampton, 6-4, 4-6, 6-2, and didn’t help herself with six double-faults.
Hampton, who needed a medical timeout for a lower back problem before she served out the second set and winced in pain, frequently on the verge of tears, throughout the third, still managed to hit 41 winners to keep the Belarusian under pressure.
Azarenka appeared frustrated at times, but overcame an early break and fended off triple break point in the seventh game of the deciding set before clinching the match in 2 hours 9 minutes.
‘‘She played incredible, went for every single shot. I felt it was touching every single line,’’ Azarenka said. ‘‘She took a medical timeout but she rips winners all over the place and I was like, ‘Can I have a back problem?’ I'm feeling great, but I'm missing every shot.’’
After wasting two set points on Azarenka’s serve late in the second set, Hampton had to leave the court for nine minutes to have treatment on her back.
Azarenka practiced her backhands and serve while Hampton was in the locker room, but the break didn’t help her immediately. Hampton returned and held in the next game and needed more treatment in the break at the end of the set.
Elsewhere, two-time major winner Svetlana Kuznetsova advanced with a 6-2, 4-6, 6-3 win over Spain’s Carla Suarez.
On Friday night, Maria Sharapova celebrated with extra exuberance after her 6-1, 6-3 win over Venus Williams, her first victory over the seven-time major winner in a Grand Slam.
‘‘I was just really pumped,’’ she said. ‘‘Why shouldn’t I be?’’
After back-to-back 6-0 wins in the first two rounds — the first time that happened at a major since 1985 — Sharapova has conceded the fewest number of games en route to the fourth round at the Australian Open since Steffi Graf did so 24 years ago.