Novak Djokovic recalled his own brush with match-fixing, as the start of the year's first Grand Slam tournament was overshadowed by corruption allegations.

Djokovic started his bid for a sixth Australian Open title with a 6-3, 6-2, 6-4 win over Chung Hyeon of South Korea on Monday, hours after the BBC and Buzzfeed News published reports alleging match-fixing had gone unchecked in tennis.

No players were identified in the reports, which alleged 16 players had been flagged repeatedly with tennis authorities but not sanctioned on suspicion of match fixing. Half of those are entered in the Australian Open, the reports said.

The governing bodies for the sport, and the Tennis Integrity Unit, issued a joint statement, read by ATP chairman Chris Kermode at a hastily-convened news conference at Melbourne Park.

Kermode said tennis authorities "absolutely reject any suggestion that evidence of match-fixing has been suppressed for any reason, or isn't being investigated."

Djokovic later responded to a question about an approach ahead of a tournament in St. Petersburg, Russia, in 2007.

"I was approached through people that were working with me at that time, that were with my team," he said. "Of course, we threw it (the approach) away right away. It didn't even get to me. The guy that was trying to talk to me, he didn't even get to me directly. There was nothing out of it.

"Unfortunately there were some, in those times, those days, rumors, some talks, some people were going around. They were dealt with. In the last six, seven years, I haven't heard anything similar."

Djokovic was an up-and-coming player at the time, not winning the first his 10 major titles until the 2008 Australian Open.

"It made me feel terrible because I don't want to be anyhow linked to this kind of — you know, somebody may call it an opportunity," he said. "For me, that's an act of unsportsmanship, a crime in sport honestly. I think there is no room for it in any sport, especially in tennis."

Djokovic said he thought the allegations related to matches from almost 10 years ago and didn't involve active players.

Roger Federer, a 17-time major winner and former leader of the player council, agreed the allegations likely weren't new but remained "super serious."

"I would love to hear names," Federer said. "Then at least it's concrete stuff and you can actually debate about it. Was it the player? Was it the support team? Who was it? Was it before? Was it a doubles player, a singles player? Which slam?

"It's super serious and it's super important to maintain the integrity of our sport. So how high up does it go? The higher it goes, the more surprised I would be, no doubt about it."

Serena Williams was on court preparing for her opening 6-4, 7-5 win over No. 34-ranked Camila Giorgi when Kermode was holding a news conference to respond to the fixing allegations.

Like Djokovic, Williams won three of the four major titles last season, but hadn't finished a competitive match for months. She withdrew from the Hopman Cup because of inflammation in her knee, playing just one set in Perth.

"I haven't played in a long time, but I have been playing for 30 years, so it's kind of — I try to focus on that," Williams said. "I was able to stay in it and stay calm today and I think that's what matters most."

The 21-time major winner said there was no hint of match-fixing on the women's tour.

"I play very hard, and every player I play seems to play hard," she said. "As an athlete, I do everything I can to be not only great, but, you know, historic."

Maria Sharapova, who lost to Williams in the final here last year and could meet her again in the quarterfinals, showed no signs of a left forearm injury that curtailed her preparations when she beat Nao Hibino 6-1, 6-3 in a night match. Genie Bouchard advanced with a 6-3, 6-4 win against Alexandra Krunic.

Two-time Wimbledon champion Petra Kvitova beat Thai qualifier Luksika Kumkhum, avenging her upset loss in the first round here in 2014, and No. 4 Agnieszka Radwanska beat Christina McHale 6-2, 6-3. Also advancing were No. 10 Carla Suarez Navarro, No. 12 Belinda Bencic, No. 13. Robert Vinci and No. 23 Svetlana Kuznetsova.

Former No.1-ranked Caroline Wozniacki lost 1-6, 7-6 (3), 6-4 to Yulia Putintseva, continuing a downward spiral at Melbourne Park that has resulted in her exiting one round earlier each year since she reached the 2011 semifinals.

No. 24 Sloane Stephens, a semifinalist in 2013, lost 6-3, 6-3 to Chinese qualifier Wang Qiang.