MELBOURNE, Australia — ATP chairman Chris Kermode and the Tennis Integrity United have rejected news reports that match-fixing has gone unchecked in the sport.

In reports published on the morning the Australian Open began, the BBC and BuzzFeed News said secret files exposed evidence of widespread suspected match-fixing at the top level of world tennis. The report said that in the last decade 16 players — all at some stage ranked in the top 50 — have been repeatedly flagged to the integrity unit.

The reports say the players — it doesn’t identify them or say whether they were involved in singles or doubles — were allowed to continue competing.

At a news conference at Melbourne Park on Monday, Kermode said officials “absolutely reject any suggestion that evidence of match-fixing has been suppressed for any reason, or isn’t being investigated.”

Nigel Willerton, head of the Tennis Integrity Unit, which was formed in 2008 as a joint initiative of the International Tennis Federation, the ATP, the WTA and the Grand Slam Board, says “it would be unprofessional for me to comment on if any players here are being monitored.”

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Serena off to good start

Defending champion Serena Williams has won her first-round match early Monday, beating Camila Giorgi of Italy, 6-4, 7-5, at Rod Laver Arena. Williams, who just missed a calendar-year Grand Slam in 2015 when she lost in the U.S. Open semifinals, was helped by 12 double-faults by the Italian player.

Williams appeared to show no soreness from recent inflammation in her left knee. “It wasn’t quick, so that actually worked to my advantage as well,” Williams said. “I think I was able to stay in it and stay calm today and I think that’s what matters most.”

No. 10 Carla Suarez Navarro advanced in straight sets, while No. 17 Sara Errani was the first of the seeded women eliminated with a 1-6, 7-5, 6-1 loss to Margarita Gasparyan. No. 24 Sloane Stephens, who beat Serena Williams in the 2013 Australian Open quarterfinals, went out in a 6-3, 6-3 loss to Chinese qualifier Wang Qiang.

No. 7 Kei Nishikori was the first of the seeded men’s players to advance, beating Philipp Kohlschreiber 6-4, 6-3, 6-3. No. 15 David Goffin had a 3-6, 6-3, 6-4, 6-4 win over Sergiy Stakhovsky, and No. 22 Ivo Karlovic was the first of the seeded players to exit the tournament when he retired due to a left knee injury in the third set while trailing Federico Delbonis 7-6 (4), 6-4, 2-1.