Serena Williams struggles into Australian Open quarters

World number two Serena Williams booked her place in the quarter-finals of the season-opening Australian Open after battling past Barbora Strycova of Czech Republic here at the Melbourne Park on Monday.

The American tennis star was tested by Strycova but she dug deep to register a 7-5, 6-4 win in the fourth-round contest that lasted one hour and 45 minutes on Rod Laver Arena.

By reaching her 11th Australian Open quarter-final, Serena has strengthened her unrelenting quest to surpass Steffi Graf's Open era record of 22 Grand Slam titles.

Serena, who lost her top ranking to Germany's Angelique Kerber last year, will now lock horns with Australia's Johanna Konta for a place in the semi-finals.

Williams, who lost last year's final to Kerber, came into the opening Grand Slam of the year with doubts over her form as she barely played since the US Open last September due to injury.

However, Serena's chances of clinching an elusive Australian Open title has improved after her rival and top-seed Kerber was stunned by America's Coco Vandeweghe 2-6, 3-6 in Sunday's last-16 round.