Nikolay Davydenko, whose loss last week at an event in Poland is under investigation due to suspicious betting patterns, beat Finland's Jarkko Nieminen 6-3, 7-6 (5) on Wednesday in the Rogers Cup.
The 26-year-old Russian, who said he felt "disappointment" when he first heard the news, was playing his first match since an injury forced him out of a match against Martin Vassallo Arguello at the Prokom Open.
"People are talking not only, say, in Russia, in my country, but everywhere in the world," Davydenko said. "It's pretty tough for me and I get more pressure for this tournament. Mentally, it's pretty tough."
He was seeded fourth and given a bye into the second round.
"I'm a professional player," Davydenko said. "I try to prepare for every match, it doesn't matter what is happening in my personal life."
British bookmaker Betfair said it received about US$7 million in bets on last Thursday's match -- 10 times the usual amount -- and most of the money was on Arguello to win, even after Davydenko won the first set 6-2.
The ATP, which is conducting the probe, said on Monday it had no plans to suspend Davydenko or ask him to sit out. The ATP confirmed that executive chairman Etienne de Villiers sent a strongly worded letter to players last weekend.
"Let's be clear on this, the board and I are committed to doing everything possible to ensure we have a clean sport," de Villiers wrote.
"The rules allow us to impose anything up to a life ban as a sanction and we will have a zero tolerance policy towards anyone found to have broken those rules. We have all seen how an issue can undermine the public's faith in other sports. We will not allow this to happen in tennis," he wrote.
US doubles player Bob Bryan told the Los Angeles Times on Tuesday that those on the men's tour have been the targets of anonymous offers to influence the outcome of matches.
"I don't know of any players that have ever gambled on tennis," said Bryan, a member of the ATP Player Council. "But there have been some anonymous calls to players' rooms with some monetary offerings. I know that. And I know every player I've talked to has turned it down."
Since 2003, the ATP has an arrangement with Betfair and the European Sports Security Association, which covers 10 online gambling companies, to get information on what are believed to be irregular gambling patterns.
In other matches on Wednesday, top seed Roger Federer celebrated his 26th birthday with a 7-6 (2), 7-6 (3) win over Ivo Karlovic. The crowd suddenly began singing Happy Birthday late in the first set, making Federer's task a little more difficult.
"I enjoy it, of course," Federer said. "At the same time you're like, `I'm struggling to get a ball back against this guy and they're singing Happy Birthday.'"
"Are they watching the same match as me?" he said.
No. 2 seed Rafael Nadal eliminated Marat Safin 7-6 (4), 6-0 in their first meeting.
Mikhail Youzhny, seeded fourteenth, defeated Stanislas Wawrinka 6-4, 6-4, but it was otherwise a difficult day for seeded players.
The No. 7 seed, Tommy Robredo, lost 6-2, 6-4 to Dominik Hrbaty, and No. 13 Andy Murray fell to qualifier Fabio Fognini 6-2, 6-2.
James Blake withdrew from the tournament before his second-round match against Lleyton Hewitt, citing abdominal problems.