Melbourne - Top seed Serena Williams staged a barnstorming comeback to reach the Australian Open quarter-finals on Monday, defeating Spain's Garbine Muguruza in a three-set dogfight.
The American 18-time Grand Slam champion beat the 24th seed 2-6, 6-3, 6-2 to set up a final eight clash with last year's finalist Dominika Cibulkova of Slovakia, seeded 11.
Williams, 33, is chasing her sixth Australian title and could lose her coveted number one ranking if she fails.
But the lacklustre starts that have plagued her this year at Melbourne Park continued against the highly rated Spanish 21-year old, who seized her chance and took the first set.
"I didn't start out so well and she did everything she needed to do in the first set, so I just decided to do my best, stay focused and relax," Williams said.
Muguruza went into the match with a 1-1 record against Williams, including bouncing her from last year's French Open, and showed no signs of nerves against the world number one.
Yelling "c'mon Serena, play better", Williams struggled for consistency, sending down two aces but committing two crucial unforced errors when she conceded a second break that gifted Muguruza the first set.
An early break in the second set was squandered when Muguruza broke back and again refused to buckle as Williams hammered away at her serve.
The American's persistence finally paid off and she broke Muguruza then belted down three straight aces to force a deciding set in style.
But she blew three break points in the opening game of the third, telling herself "relax, relax" after shanking a forehand wide.
It was then Williams' turn to come under pressure, surviving six break points in a game that stretched almost 15 minutes, then comfortably breaking the Spaniard in the next.
It proved a turning point, with
the dispirited Muguruza offering little further resistance as Williams
wrapped up the match in exactly two hours.