World number three Jelena Jankovic ended the hopes of home favourite Casey Dellacqua 7-6 6-1 on the Rod Laver Arena to reach the quarter-finals of the Australian Open for the first time.

The Serbian snatched a topsy-turvy first set 7-3 on the tie-break before cruising through the second to line up a meeting with defending champion Serena Williams.

Dellacqua, who beat former world number one Amelie Mauresmo in the previous round, matched Jankovic in the first set as she forced a tiebreak.

But the Serbian broke early in the second set and after winning a long service game to lead 4-1, eased to victory.

Earlier in the day, champion Williams had applied the pressure when she need to and withstood a tough fourth-round challenge from Nicole Vaidisova to reach the last eight.

The American seventh seed won the match 6-3 6-4 after being forced to dig deep in the second set when her 12th-seeded Czech opponent attempted to force a decider.

However, just as the rangy Vaidisova looked to capitalise on a second set break of serve, the American broke immediately back to go ahead 5-4 with the opportunity to serve for the match.

The 18-year-old Vaidisova, who smashed her racket on the court at the end of that game, was seen talking to herself constantly during the changeovers.

Williams then capitalised on the teenager's frustration and served to love to seal victory.

Reuters