Melbourne (AFP) - Five things we learned from the Australian Open, the first Grand Slam tournament of the tennis season:

- Men's tennis needs a rivalry

The world is impressed and amazed by Novak Djokovic's dominance but it isn't much fun watching him trample over his competitors time and time again. The wins keep coming for the Serb and his ruthless recent treatment of Rafael Nadal, Roger Federer and Andy Murray, in Sunday's one-sided final, underline his supremacy after what was a dominant 2015. Djokovic's main threat is now time, as he pursues Federer's all-time record of 17 Grand Slam titles, and, he says, the karmic forces that keep his feet on the ground. "You can get a big slap from karma very soon," he warned. But tennis is a sport of two players and Djokovic needs a true competitor across the net to make his matches truly compelling. John McEnroe and Jimmy Connors, Federer and Nadal are rivalries which caught the imagination and made tennis fans tune in. Djokovic clinically dismantling Murray 6-1 in the first set of a Grand Slam final isn't quite the same.

- Serena's not a robot

Serena Williams has come to dominate women's tennis so completely that in the women's final, few gave Angelique Kerber any hope at all. But in a mesmerising two hours and eight minutes at Rod Laver Arena, the German confounded all expectations as she handed the world number one her first defeat after six previous victories in the Melbourne final. It capped a women's competition that was full of drama, with world number two Simona Halep knocked out in the first round and Naomi Osaka and Zhang Shuai enjoying a dream tournament along with Johanna Konta, who became the first British woman since 1983 to reach a Grand Slam semi-final. Kerber's win also set up the women's season nicely as, along with becoming the sport's newest Grand Slam champion, it left Williams with work to do to win the Grand Slam title that will put her level with Steffi Graf's Open-era record of 22. The American appeared tortured by expectations as she fell agonisingly short of a calendar-year Grand Slam last year, and she seemed almost relieved when her chances of another attempt at a clean sweep were blown away by Kerber. "As much as I would like to be a robot, I'm not. I try to. But, you know, I do the best that I can," Williams said. "I try to win every single time I step out there, every single point, but realistically I can't do it."

- Nadal's problems haven't gone away

We didn't see much of Rafael Nadal in Melbourne, but the fact he was bundled out in the first round does not augur well for the 14-time Grand Slam champion. Nadal endured a miserable season in 2015 but there were signs of life when he recovered to end the year on a positive note. But 2016 hasn't started well for Nadal, who was thrashed 6-1, 6-2 by Novak Djokovic in the Doha final and then was beaten 7-6 (8/6), 4-6, 3-6, 7-6 (7/4), 6-2 by Fernando Verdasco in his first match of the Australian Open. The tournament has previously been problematic for Nadal, who has been hit by injury more than once in Melbourne, and the match-up with his fellow Spanish left-hander is a tough one, producing a classic semi-final in 2009. But it seems Nadal remains nowhere near the form that made him the terror of the courts for so many years. Australian legend Rod Laver said it best when he observed: "Potentially his forehand doesn't seem to be as good as it was three and four years ago. That heavy topspin, that speed he put on the ball. You know, the ball jumps; he hit it deep; he was on the offensive all the time. It just seems that he's not quite the same when he's hitting that shot. It's more keeping it in play, not trying to be really attacking."

- Tennis has a corruption problem

It wasn't news to those in the know, but to everyone else it came like a rocket: tennis matches are preyed on by match-fixers, and players who have been in the top 50 have repeatedly fallen under suspicion without facing action, according to a bombshell report by the BBC and BuzzFeed. It sparked a flurry of revelations and accusations, with Djokovic among the players to confirm a match-fixing approach early in his career. The report was initially greeted with barely disguised irritation by tennis authorities, but as the controversy snowballed they wisely took action and announced an independent review of the sport's under-fire corruption-fighting body. Tennis thus used a damaging scandal to paint itself in a favourable light, unlike other sports which have become mired in scandal in recent months.

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