Novak Djokovic, Stan Wawrinka and Serena Williams advanced to the quarterfinals of the 2015 Australian Open in Melbourne, Australia.

Djokovic, who is aiming to win his fifth Australian Open title, cruised to the quarterfinals with a hard-earned 6-4 7-5 7-5 victory against a determined Gilles Muller of Luxembourg.

Muller managed to post threat to Djokovic in the match, but the top-seeded Serb was on target on Monday morning, hitting 47 winners, saving four break points and only had 16 unforced errors in his victory.

"I think I have to take the positives from tonight and definitely what stands out is the serve," said Djokovic, who advanced to his 23rd consecutive Grand Slam quarterfinal. "I got a lot of aces, got a lot of free points there. That's something that obviously encourages me for the rest of the tournament."

Djokovic, who has not dropped a set in the tournament, will go up against eighth seed Milos Raonic of Canada in the quarterfinals. Raonic moved on to the final eight with a 6-4 4-6 6-3 6-7(7) 6-3 victory over Feliciano Lopez of Spain.

Meanwhile, defending champion Stan Wawrinka also cruised to the quarterfinal after defeating unseeded Guillermo Garcia-Lopez of Spain 7-6(2) 6-4 4-6 7-6(8) in their fourth-round match.

Wawrinka, who won last year's Australian Open by defeating Rafael Nadal in the final, was on the verge of losing in the fourth set as Garcia-Lopez looked poised to extend the match into a fifth set.

However, Wawrinka managed to save four set points in the final tiebreaker of the match, erasing a 6-2 deficit and saving another set point en route to the fourth-round victory.

Wawrinka, who avenged his defeat to Garcia Lopez in the first round of the 2014 French Open, will face fifth seed Kei Nishikori of Japan in the quarterfinals. Nishikori edged ninth seed David Ferrer 6-3 6-3 6-3 in their fourth-round match on Monday morning at Rod Laver Arena.

On the women's side, Serena Williams struggled to find her rhythm in the opening set of her match against Garbine Muguruza of Spain, but the top seed bounced back and scored a 2-6 6-3 6-2 win to reach the quarters.

Williams will face 11th seed Dominika Cibulkova of Slovakia in the quarterfinal. Cibulkova advanced to the next round with a hard-earned 6-2 3-6 6-3 win against Victoria Azarenka of Belarus.

Complete 2015 Australian Open Day 8 Results are available on this link, while more match highlights can be seen here.

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