Smooth sail for Djokovic and Williams

 Novak Djokovic and Serena Williams launched their Australian Open campaigns in style on Tuesday as Ivo Karlovic smashed a record 75 aces in an unprecedented 84-game marathon.

Djokovic and Williams have both dropped to world number two and faced awkward opposition, but they won in straight sets against Fernando Verdasco and Belinda Bencic respectively.

Rafael Nadal also rolled into round two before Karlovic outlasted Horacio Zeballos in an epic that stretched for five hours, 15 minutes and ended 6-7 (6), 3-6, 7-5, 6-2, 22-20.

Karlovic beat Thomas Johansson's Australian Open record of 51 aces in a match, set in 2005, and 84 games was a new mark for the tournament in the tiebreak era, edging the 83 in Andy Roddick’s 2003 defeat of Younes El Aynaoui.

It was one of the longest matches in the tournament's history in terms of time, although still short of the five hours, 53 minutes played by Djokovic and Nadal in the 2012 men's final.

The denouement, when it finally came, was almost comical as an exhausted Karlovic chipped a hopeful lob over Zeballos, only for the Argentine to send a wayward forehand rocketing out of the court.

As the drama played out on Court 19, Djokovic gave further evidence of his return to form as he convincingly saw off Verdasco 6-1, 7-6 (4), 6-2 on Rod Laver Arena.

Djokovic fell off the top of the rankings during a sudden slump last year but he showed signs of a revival by beating new world number one Andy Murray in this month's Doha final.

He fended off five match points against Verdasco in the Doha semis, and had to fight through a 71-minute second set against the Spanish left-hander for his win on Tuesday.

It was Djokovic's 15th straight win at the Australian Open as he seeks his third straight title and his seventh overall, which would break Roy Emerson's record set in the 1960s.

In afternoon play, Williams and Nadal made light of hot temperatures and doubts over their own form as they got off to sizzling starts.

Williams, back after an injury lay-off, demolished the dangerous Bencic 6-4, 6-3, while Nadal was also impressive in his 6-3, 6-4, 6-4 win over Florian Mayer.

Williams has barely played since her shock defeat in the US Open semifinals in September and she made, by one count, 88 unforced errors in her second-round loss to Madison Brengle at this month's Auckland Classic.

But she came through a tight first set against Bencic before dominating the second in what turned out to be an emphatic victory on the centre court.

The 35-year-old American, with a record 23rd major title in her sights, was watched from courtside by her new fiance, Reddit co-founder Alexis Ohanian.

Williams next faces Lucie Safarova, who saved nine match points before beating Yanina Wickmayer.

Men's world number three Milos Raonic, a semi-finalist last year, enjoyed an uncomplicated start to his campaign when he beat Germany's Dustin Brown 6-3, 6-4, 6-2.

And German hotshot Alexander Zverev credited a racquet-smashing tantrum with a sparking revival as he came back to beat Robin Haase 6-2, 3-6, 5-7, 6-3, 6-2.

Injury-hit Nadal had a torrid 2016, failing to reach any of the Grand Slam quarterfinals, but he appeared rejuvenated under new coach and former world number one Carlos Moya.

In the final match on centre court, Polish third seed Agnieszka Radwanska beat Bulgaria's Tsvetana Pironkova, 6-1, 4-6, 6-1.

Meanwhile, Poland's Agnieszka Radwanska survived a dogfight to move into the second round as she bids to end her long wait for a maiden Grand Slam title.

The third seed battled past fellow veteran, Bulgarian Tsvetana Pironkova, 6-1, 4-6, 6-1 and will next play Croat Mirjana Lucic-Baroni, who beat Chinese qualifier Wang Qiang in three sets.