Serena Williams reaches quarters

— -- MELBOURNE, Australia -- Serena Williams avenged her heaviest Grand Slam defeat with a comeback 2-6, 6-3, 6-2 win over Garbine Muguruza on Monday to reach the Australian Open quarterfinals.

The top-ranked Williams was pushed all the way by No. 24-seeded Muguruza, who matched her in the heavy-hitting rallies, and who had conceded only four games to her in a second-round upset last year at the French Open.

Five-time Australian Open winner Williams next faces Dominika Cibulkova, who reproduced the kind of tennis that helped her reach the final here last year as she beat two-time champion Victoria Azarenka 6-2, 3-6, 6-3.

Williams appeared to be laboring at times, and had a serious cough. She struggled with her serve in the first set, winning only one of a dozen points on her second serve as the 21-year-old Spaniard went on the attack. She couldn't convert her six break-point chances, while Muguruza broke her twice.

"She hits the ball really, really big, really, really hard," Williams said. "Someone in the crowd was like 'C'mon Serena use spin' and I was like 'OK.' There's coaches everywhere out here! Thank you."

Williams hasn't advanced past the quarterfinals at Melbourne Park since winning her last title here in 2010.

There was a lot to distract her. In the first set, six planes were doing coordinated loops and tricks in the sky over Rod Laver Arena, as part of the national day celebrations in downtown Melbourne. She had difficulty breathing at times, and had a heaving coughing fit into a towel at a changeover.

"I've been a little sick the past couple days but I just love it here," Williams said, when asked if she'd swallowed a fly. "When I got down, I was thinking, `'What can I do now?' Whatever happens, I thought, I've won this five times."

She gradually picked up power in the second set, broke for a 5-3 lead and then fired three aces and a service winner to level the match at 1-1, screaming as she pumped her fist.

After missing break points on Muguruza's serve in the opening game of the third, Williams saved six break points and needed almost 13 minutes to hold.

Her confidence up, Williams broke for a 3-2 lead and dominated the rest of the match.

She'll need every bit of confidence against the 1.61-meter (5-foot-3) Cibulkova, who pounded 44 winners and broke former No. 1-ranked Azarenka's serve seven times to reach a Grand Slam quarterfinal for the sixth time.

The No. 10-ranked Cibulkova lost the final here last year to the now-retired Li Na, and is back in that kind of form.

"I just walked onto the court and all great memories came to my mind," she said, reflecting on how her run last year is inspiring her at the Australian Open, "I thought 'I'm a great player and I can do it."

"As you can see, I'm not the tallest player on tour, I need to have something extra if I want to beat these top players," she said of her heavy groundstrokes. "This is my energy on the court, this is how I play."

  Madison Keys advanced to her first Grand Slam quarterfinal with a 6-2, 6-4 win over good friend and fellow American Madison Brengle.

The 19-year-old Keys dominated the match, hitting 38 winners to just three for Brengle and breaking her opponent four times.

It was the first time since Jennifer Capriati played Amy Frazier at the 2002 U.S. Open that two Americans besides the Williams sisters played each other this late in a Grand Slam.

Keys said after the match, "You know it's always hard just even being in this situation, then on top of it playing a friend."

Keys, who had never previously been beyond the third round of a major, is now coached by three-time major winner Lindsay Davenport.

Azarenka, unseeded this year after her ranking slipped into the 40s following an injury-interrupted 2014, won the Australian title in 2012 and '13 and reached the quarterfinals last year. She opened the tournament with a win over 2013 semifinalist Sloane Stephens and then defeated No. 8-seeded Caroline Wozniacki -- the U.S. Open finalist last year and former No. 1 -- and No. 25 Barbora Zahlavova Strycova.

Rain showers forced the roofs on all three stadium courts to be closed early, but they opened for later matches when the weather cleared.

Information from The Associated Press was used in this report.