NEW YORK (AP) — Rafael Nadal's next opponent at the U.S. Open is a 28-year-old from Ukraine who is being asked questions about a different tournament entirely — one where he was involved in a match under scrutiny from anti-corruption investigators because of unusual betting.

Alexandr Dolgopolov moved into the fourth round at Flushing Meadows for the first time since 2011 with a victory Saturday. Dolgopolov, who is ranked 64th, said after his 6-1, 6-0, 6-4 win against Viktor Troicki that he has been interviewed by the Tennis Integrity Unit.

That group is looking into a match he played against Thiago Monteiro at a hard-court event in Winston-Salem, North Carolina, on Aug. 20.

Dolgopolov said he approached the TIU.

"I was the first one to come there and try to give them all the information, so they can investigate it faster," he said.

Asked what the TIU has told him about its work, Dolgopolov replied: "I don't know. I don't ask. They asked me about some information. They interviewed me. That's it. That's all I can do."

As for what effect the whole episode has had on him, Dolgopolov said: "Not much. You can see I'm playing. I'm fit. I'm doing well. Obviously it's disappointing, but not more. If people want to write something, they write something. You can't stop them from doing it. It's just not under my control."

TIU spokesman Mark Harrison said this week that the group "was made aware of concerns over betting patterns" during the match between Dolgopolov and Monteiro. The match is being assessed but is not yet under formal investigation, Harrison said, noting that many reasons other than corruption can explain unusual gambling patterns.

Dolgopolov certainly has looked good on court at the U.S. Open.

He beat 2010 Wimbledon finalist Tomas Berdych in the second round, then needed less than 1½ hours to eliminate Troicki in the third.

Dolgopolov's best Grand Slam showing was a run to the Australian Open quarterfinals in 2011. Later that season, he lost to Novak Djokovic in the fourth round in New York.

Now comes the spotlight associated with a match against the top-seeded Rafael Nadal, whose 15 Grand Slam titles include two at Flushing Meadows. Nadal advanced Saturday night by beating Leonardo Mayer 6-7 (3), 6-3, 6-1, 6-4 with the Arthur Ashe Stadium roof closed because it was raining.

"I'm not a young player anymore," Dolgopolov said. "I don't think I'm going to get intimidated by the No. 1 player or the stadium or the occasion."

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