A white towel over his shoulders and a grim look on his face, Nikolay Davydenko autographed three balls and hit them into the stands Monday after winning his first-round match at the U.S. Open.

The man at the center of tennis' gambling probe, the No. 4-ranked Davydenko has plenty on his mind besides smacking fuzzy yellow spheres these days. The Russian has not been questioned by ATP or outside investigators yet, but he expects to talk to them sometime when his schedule winds down after the Sept. 10-16 China Open.

"I got tired mentally in this situation," Davydenko said after beating Jesse Levine of the United States 6-4, 6-0, 6-1, "and I don't know if I will be able to regain my strength to fight and play well here."

In early August, the ATP began an investigation after a British online gambling company, Betfair, voided all bets on a second-round match between Davydenko and 87th-ranked Martin Vassallo Arguello of Argentina at Sopot, Poland.

Betfair received about $7 million in wagers on the match, 10 times the usual amount. Most of the money backed Arguello -- including bets placed after he lost the first set to Davydenko, a semifinalist at the French Open twice and at the U.S. Open last year. Davydenko wound up winning the second set, then retiring in the third with a left foot injury.

Nearly every question Davydenko was asked at his postmatch news conference Monday was about this one issue. As in recent weeks, he again denied any role.

"Never (bet) in my life," he said. "I don't know how you can (bet), and I don't know guys who (bet). ... I try to say every week, 'I don't do anything like this.' You know, I never did."

In the wake of the investigation, some men on the tour said word spread of past instances of players being approached about throwing matches.

"I have heard of stories of people getting sometimes money offered for losing a match and stuff. A lot of money," top-ranked Roger Federer said recently. "So this is why it's hard and this is where we have to have faith in the players saying they don't want to accept this type of money because it's bad money."

Davydenko was asked about whether the Russian mafia has any influence in the sport.

"First, I don't live in Moscow. I don't know really guys from mafia in Russia, because I live from 15 years old in Germany. I don't know German mafia," he said with a smile. "Maybe if you go now to Brooklyn, you find Russian mafia here in New York."

ATP rules say players and their "support personnel" can't bet on any amateur or professional tennis matches. They also are not allowed to, "directly or indirectly, solicit, induce, entice, persuade, encourage or facilitate any other person to wager on the outcome or any other aspect of any event."

Under the ATP's anti-corruption system set up in 2003, players can be fined $100,000 and be barred permanently from playing in tour events. No player has been sanctioned under that program, according to the ATP.

"I'm pretty confident it's an isolated event. Until we know something, until due process takes its course, you can't really say anything. It would worry me if they found there was something going on and nothing happened then," 2003 U.S. Open champion Andy Roddick said.

"But it's disappointing. You don't want to hear about it," he continued. "You don't want tennis' story lines to be that."

The Davydenko case, along with the recent NBA scandal involving a former referee who admitted betting on games he officiated, prompted the U.S. Tennis Association to hire a security firm to monitor illegal gambling activity during the U.S. Open.

The Grand Slam tournaments are talking with the men's and women's professional tours to design a joint antigambling program.

In the meantime, the ATP's investigation is being kept under wraps.

"This is going to be comprehensive, thorough but fair. We're not going to leave any stone unturned," ATP spokesman Kris Dent said. "This is not an overnight investigation. ... It's going to take a fair amount of time. We're not talking weeks here."

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