MELBOURNE, Australia — Serena Williams and Victoria Azarenka advanced in contrasting styles Saturday to the fourth round at the Australian Open.

Williams, the tournament favorite 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.

Azarenka, the top-ranked defending champion, struggled to hold off injured American Jamie Hampton 6-4, 4-6, 6-2 — and she didn’t help herself with six double-faults.

At least she survived.

Juan Martin del Potro, the 2009 U.S. Open champion, lost a marathon match 6-3, 6-3, 6-7 (3), 3-6, 6-3 to Jeremy Chardy of France, leaving only three major winners in the men’s draw.

Andy Murray, who joined the ranks of the Grand Slam winners at last year’s U.S. Open, advanced with a gritty 6-3, 6-4, 7-5 win over Lithuanian qualifier Ricardas Berankis.

“I feel so much emotion. Five sets, to be here in a Grand Slam. It’s the most beautiful match of my career,” Chardy said. “It’s a great moment for me, everyone dreams of this.”

Second-ranked Roger Federer, who has four Australian titles among his record 17 majors, was playing Bernard Tomic later Saturday after No. 1 Novak Djokovic took another step toward his third consecutive Australian title with a third-round win Friday.

After taking del Potro out of the top section of the draw, Chardy will next face No. 21 Andreas Seppi of Italy, who ousted No. 12 Marin Cilic with a 6-7 (2), 6-3, 2-6, 6-4, 6-2 victory.

A pair of Frenchmen advanced and will meet in the fourth round, with No. 7 Jo-Wilfried Tsonga beating Slovenia’s Blaz Kavcic 6-2, 6-1, 6-4 to set up a meeting with No. 9 Richard Gasquet, who fended off Croatia’s Ivan Dodig 4-6, 6-3, 7-6 (2), 6-0.

Williams surprised herself with another serve at 128 mph in an afternoon match on Rod Laver Arena, matching a career best that she hit earlier in the tournament.

“I tried to hit it really hard. I hit 207 (kph) the other day and I thought it was luck,” she said. “But I did it again and I was like, ‘Whew! I’m going to try to go for 210.’ We’ll see.”

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.

Hampton needed a medical timeout for a lower back problem before she served out the second set. She winced in pain and was frequently on the verge of tears throughout the third set, but still managed 41 winners to keep the Belarusian under pressure.

“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.

Even with the pain of two herniated disks, the 23-year-old Hampton, from Auburn, Ala., went down swinging — making 47 unforced errors to go with the winners that caught Azarenka off guard and had her asking, loudly at one point, what she could do to counter them.

Sensing an upset, and stirred by the obvious signs of pain, the crowd in Rod Laver Arena got right behind the No. 63-ranked Hampton, who had never previously gone past the second round at a major.

Azarenka had her share of supporters in the stands, too, including friend and musician RedFoo, who was wearing a shirt emblazoned with “We Go Hard” across the front.

If results go according to rankings, Azarenka and Williams will meet in the semifinals. Williams has won the Australian Open five times and is on a 19-match winning streak — and she has lost only one match since her first-round exit at the French Open last year.

Considering Azarenka has lost 11 of their 12 meetings, including all five in 2012, it’s a potential matchup where Azarenka will have to play better than ever. But they both have to advance to the last four, something Williams failed to do here last year when she was knocked out in the fourth round.

In this year’s fourth round, the 31-year-old American will meet No. 14 Maria Kirilenko, who beat No. 20 Yanina Wickmayer 7-6 (4), 6-3. Azarenka next plays Elena Vesnina, who beat 16th-seeded Roberta Vinci of Italy 7-6 (4), 6-4.

Two-time major winner Svetlana Kuznetsova continued her comeback from injury with a 6-2, 4-6, 6-3 win over Spain’s Carla Suarez Navarro and advanced to a fourth-round match with former No. 1 Caroline Wozniacki, a 6-4, 6-3 winner over Ukrainian qualifier Lesia Tsurenko.