Denis Istomin of Uzbekistan stunned Serbia's world No. 2 Novak Djokovic with a 7-6(8), 5-7, 2-6, 7-6 (5), 6-4 victory in a match at Rod Laver Arena in that took almost five hours to complete. This was the six-time Australian Open champion's earliest exit from Melbourne Park since his first round elimination in 2006.

The 30-year-old Istomin let out a roar of delight after Djokovic sent a service return long to end the contest after four hours and 50 minutes on the court.

"First of all I feel sorry for Novak. I was playing so good today," the 117th-ranked Istomin said in the on-court interview.

"I mean, I surprised myself also today. I want to thank my team ... who do a good job. Amazing! So much emotion on my mind so I cannot hold it you know but I want to say thanks very much for coming to support me."

The wildcard, who hit 63 winners, edged the first set but simply refused to fold when the former world No. 1 came back to win the second and third sets.

Having clinched the fourth on a tiebreaker to send the match into a decider, Istomin grabbed an early break in the fifth and held his nerve to take the match.

"I mean it was tough, since third set I get cramping in my leg so I don't know how I hold it," Istomin said. "But I was physically normal today."

The Uzbek is to face Spanish 30th seed Pablo Carreno Busta in the third round.

Nadal to face 'future No.1' in third round

Ninth-seeded Rafael Nadal, who is looking for a better year after an injury-riddled 2016 kept his bid for a 14th Grand Slam and second Australian Open title alive by beating the 36th-ranked Marcos Baghdatis 6-3, 6-1, 6-3.

"When you have been away, off the tour for a while, you need to come back. The thing that you need is to win," Nadal said in the on-court interview.     

"I know I have been working great. I know I have been working a lot and very well. I have been practicing at high level. So every time that I have the chance to go on court, I am able to have more confidence on what I'm doing."

Nadal's victory set up an enticing third-round matchup, which will see him face rising German star Alexander Zverev.

"It will be a high-quality match against a potential Grand Slam winner and a future world No. 1," said of his match with the 19-year-old Zverev. The younger of the Zverev brothers had advanced earlier by beating 18-year-old Frances Tiafoe of France, 6-2, 6-3, 6-4.

The other German man, still in the tournament, Philip Kohlschreiber, also advanced, beating the American, Donald Young 7-5, 6-3, 6-0.

Raonic, Monfils through

Also on Thursday, the No.3 men's player, Milos Raonic of Canada, needed four sets to beat Luxembourg's Gilles Muller, 6-3, 6-4, 7-6, 7-4, and sixth-ranked Gael Monfils dispatching Oleksandr Dolgopolov Jr. 6-3, 6-4, 1-6, 6-0. Monfils now moves on to face Kohlschreiber in the third round.

Women's third seed eliminated

There was another upset later on Thursday, this time on the women's side, as the third seed and former semifinalist, Agnieszka Radwanska, was knocked out of the second round by Croatia's Mirjana Lucic-Baroni.

The 79th-ranked Lucic-Baroni left beat Radwanska in straight sets, 6-3, 6-2 in their late-afternoon match.

Radwanska, who reached the semifinals at Melbourne Park in the previous two years, slumped to her earliest exit at the Australian Open since her first-round elimination in 2009.

The German-born Lucic-Baroni, 34, is to face Frenchwoman Alize Cornet or Maria Sakkari of Greece in the third round.

Serena moves on

The women's second seed, Serena Williams, then swept past Lucie Safarova and into the third round to keep her Grand Slam record hunt on track. The American, who is chasing her 23rd major title, powered past Safarova 6-3, 6-4.

Germany's Andrea Petkovic had a disappointing outing against Barbora Strycova of the Czech Republic, losing 6-0, 7-5.