He played his first match in the Grandstand. His second, third, and fourth inside Louis Armstrong Stadium. Yesterday, inside Arthur Ashe Stadium for the first time, he did what he has done for the last 10 days: Pummel tennis balls, rarely miss, and win in straight sets, this time 6–3, 6–3, 6–4 over Tommy Haas. He is Nikolay Davydenko, the no. 4 player in the world, and he won’t do what most people wish he would, go away.

Davydenko, famous these days for suspicious gambling activity surrounding a match he played in Poland this summer, hasn’t let the persistent questions about whether he threw a match stop him from playing his best U.S. Open to date.

Davydenko reached the semifinals last year, when he beat Haas in the quarterfinals despite losing the first two sets. This year, he trampled the German in two hours and 24 minutes, hitting 42 winners and making only 19 errors. Haas tried to win baseline rallies and couldn’t. He tried to serve and volley and attack the net, and though this worked at times, it didn’t often enough. The volatile Haas, who defeated James Blake and had played four more hours of tennis than Davydenko when the match began, barely had the energy for temper tantrums, just a few racket tosses and curses, followed by resignation. Davydenko, the man with the short, powerful strokes and quick feet, wasn’t going to let up.

“No mistake, I think is most important,” Davydenko said.

“I don’t know how he does it,” Haas said. “You wonder sometimes.”

People have been wondering about Davydenko all summer, but for more troubling reasons. In Sopot, Poland, the Russian won the first set and lost the second against a low-ranked opponent, Martín Vassallo Argüello. Although Davydenko, the tournament’s defending champion, seemed to be having an easy time, gamblers bet heavily against him, even after he won the first set. He eventually retired with an injury, and Betfair, the online betting company that took the bets, canceled them. The men’s tour has since begun an investigation and will interview Davydenko later this month. Meanwhile, several players have said they were approached by people who offered money to fix matches.

Davydenko has denied any involvement, saying that perhaps word had gotten out about his injury via a trainer or someone at the tournament. The whiff of scandal certainly hasn’t affected his play, which has been consistent all season: He also reached the quarterfinals at the Australian Open and the semifinals at the French Open, where he played Roger Federer close for three sets.

It’s this consistency, of course, that makes many people skeptical of Sopot. Davydenko may never rise above his ranking — he has a career record of 12-–5 against top 10 players has never beaten either of his next opponents, Federer (0–9) or Andy Roddick (0–4) — but he rarely plays below it. All the more reason to wonder, and to hope that the tour finds out what happened there, and soon.