World number one Novak Djokovic reached the Australian Open third round with a straight-set win over Jo-Wilfried Tsonga.

The six-time champion in Melbourne beat the 33-year-old Frenchman 6-3 7-5 6-4.

Tsonga, whose ranking has fallen to 177 after a knee injury restricted him to 12 matches in 2018, showed flashes of his ability but the Serb, 31, was always in control.

Djokovic faces 19-year-old Canadian Denis Shapovalov, the 25th seed, next.

The match against Tsonga was a repeat of the 2008 final in Melbourne, which the Serb won in four sets to secure his first Grand Slam title.

“You could feel the tension on court at the beginning. We felt a lot of emotion and tried to play a great game,” said Djokovic.

“It’s always tough to play Jo. He has struggled with injury and his ranking doesn’t do him justice in my eyes.”

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Eighth seed Kei Nishikori survived a fightback from Ivo Karlovic to win a final-set tie-break and reach the third round of the Australian Open.

The Japanese player took a two-set lead, before 39-year-old Karlovic, who served 59 aces, recovered to force a decider on Margaret Court Arena.

Nishikori held his nerve to edge out the Croat 6-3 7-6 (8-6) 5-7 5-7 7-6 (10-7) in three hours and 48 minutes.

Meanwhile, Milos Raonic beat 2014 champion Stan Wawrinka in four sets.

Raonic will face Pierre-Hugues Herbert in round three after the Frenchman beat 24th seed Chung Hyeon 6-2 1-6 6-2 6-4.

The South Korean, who reached the semi-finals at Melbourne Park last year, is likely to drop out of the world’s top 50 after the tournament.

Seventh seed Dominic Thiem retired injured from his match against wildcard Alexei Popyrin when trailing 7-5 6-4 2-0.

The Austrian, who had shown signs of frustration that boiled over into smashing his racquet, had come through a draining five-setter in his opening match against Benoit Paire and never looked comfortable against 19-year-old Australian Popyrin.

“I felt very bad during the game, obviously,” Thiem said.

“I started to feel like my whole body hurt, generally not feeling well at all, and in the match it got worse. [My] whole body was hurting, I was feeling weak, and there was no sense to continue.”

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Nishikori saved three break points at 4-4 in the final set and was then 6-7 down in the decisive tie-break, as Karlovic stood on the brink of becoming the oldest man to reach the third round since 44-year-old Australian Ken Rosewall in 1978.

“It was a tough match which could have gone both ways. He almost had it for sure,” said Nishikori, a three-time quarter-finalist at Melbourne Park,

“I focused well on the last points, I’m very happy to win. We both played great tennis – of course he served really well.”

He faces Joao Sousa after the Portuguese beat Philipp Kohlschreiber 7-5 4-6 7-6 (7-4) 5-7 6-4.

Canada’s Raonic was forced to come from a set down to see off Swiss three-time Grand Slam champion Wawrinka, who was unseeded for the first time since his debut in 2006 after injuries saw him drop to 59th in the world.

Raonic, the 16th seed, won 6-7 (4-7) 7-6 (8-6) 7-6 (13-11) 7-6 (7-5) in four hours one minute.

“It feels like four hours passed by in about 15 minutes,” he said.

“It was the heat of the battle – the adrenaline takes over and I was fortunate to stay alive in that fourth set.

“I am thankful I was able to play a good match.”

Frenchman Gilles Simon, the 29th seed, was beaten in five sets by Australian wildcard Alex Bolt, who is ranked 159th in the world.

In a match lasting more than four hours, Bolt won 2-6 6-4 4-6 7-6 (10-8) 6-4 to set up a third-round encounter with fourth seed Alexander Zverev or Frenchman Jeremy Chardy.

Former Australian Open champions Jamie Murray and Bruno Soares reached the second round in Melbourne after seeing off Roman Jebavy and Andres Molteni.

Britain’s Murray and Brazilian Soares, winners in 2016, clinched a mammoth tie-break in the second set to beat the Czech-Argentine pair 6-4 7-6 (13-11).

The third seeds face all-British duo Luke Bambridge and Jonny O’Mara next.

Cameron Norrie and American Taylor Fritz, whom the Briton lost to in the singles first round, also advanced.

They beat Bosnia & Herzegovina’s Mirza Basic and Damir Dzumhur 7-6 (9-7) 7-5 to set up a meeting with Jack Sock and Jackson Withrow.

Americans Sock and Withrow stunned second seeds and 2018 runners-up Juan Sebastian Cabal and Robert Farah of Colombia 6-7 (6-8) 6-3 6-4.

Britain’s Ken and Neal Skupski also progressed, beating Australians James Duckworth and Jordan Thompson 6-3 6-4.

They will take on Finland’s Henri Kontinen and Australian John Peers in the second round.

Meanwhile, Britain’s Joe Salisbury also made it through alongside American Rajeev Ram, winning 6-0 6-4 against Argentine Guido Pella and Chile’s Hans Podlipnik-Castillo.

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Andy Murray has criticised British tennis for failing to translate his achievements into grassroots growth in the sport at home.

The 31-year-old’s future is in doubt as he contemplates further hip surgery.

The three-time Grand Slam winner says not enough has been done by the Lawn Tennis Association to build on British success in recent years.

“I’m not sure Britain has really capitalised on the last seven or eight years of success we’ve had,” he said.

“Whether it be myself, my brother, Jo [Konta], Kyle [Edmund], the Davis Cup, those sorts of things, I’m not sure how much we’ve done there.

“There are quite a few players coming through that have potential to go on and do better, but obviously you are talking about the high end of the game.”

Murray, who was beaten in an emotional five-set match by Spain’s Roberto Bautista Agut in the first round of the Australian Open on Monday, has been at the forefront of the sport in Britain since coming through as a junior, but has been critical of the sport’s governing body on many occasions.

In 2015 after Britain’s first Davis Cup victory since 1936, the Scot said talking to the LTA about the future of British tennis was “a waste of his time” and that “nothing ever gets done”.

He is concerned that when he retires, an opportunity will have been missed to grow the sport.

“Maybe it’s something I should have given more thought to while I was playing but I never felt that was my job to do that,” he added.

“It is a little bit disappointing. I don’t understand how in the last eight to 10 years that participation is dropping – I don’t get it.

“I know in Scotland that there have not been many indoor courts built in the last 10 years. That seems madness. I don’t understand why that is.

“You need to get kids playing; you need to have the facilities that allow them to do that.”

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The LTA said: “Andy Murray is not just the greatest British tennis player of all time, but one of the greatest sports people this country has ever produced.

“But his impact for our sport goes far beyond his own trophy cabinet.

“It has transcended tennis and taken the British people’s interest and excitement in tennis to levels not seen before and the LTA is determined to translate his inspiration into a lasting legacy.”

Murray’s older brother Jamie, who starts his Australian Open doubles campaign on Thursday, said: “My greatest worry was that he would stop one day, which obviously feels like it’s been probably accelerated, and you would look around the country and there wouldn’t be much to show for it.

“If you go around the country you probably see that.

“It is sad because how on earth are you going to grow a sport if you can’t do it when you’ve got one of the biggest stars in tennis for the last 10 years, and one of Britain’s most prominent sportspeople?”