KEY BISCAYNE, Fla.— Nikolay Davydenko's grunts became a little louder in the last game today, and the extra effort helped him finish off Rafael Nadal in the final of the Sony Ericsson Open.

With a 6-4, 6-2 victory, Davydenko became the first Russian to win the Key Biscayne men's championship.

The title is Davydenko's first this year while playing under the cloud of an ATP investigation into heavy wagering on a match he lost last August at an obscure tournament in Poland. He retired in the third set, citing a foot injury, and says he did nothing wrong. For months he has accused the ATP of dragging out the investigation.

There was no question about his effort against Nadal. Davydenko broke at love to take the lead for good at 4-3 in the first set, and in the second set he lost only two of 19 points on his serve to pull away.

When the No. 4-seeded Davydenko belted one final forehand winner on championship point, he grinned and shook his fists, then punched the air. During the trophy ceremony, he said he didn't believe he had won.

"For me it's surprising standing here," he said. "It's crazy."

Davydenko overcame a match point in each of his first two matches and became the fourth ATP player in 2008 to win a title after facing match point. He beat Andy Roddick in the semifinals.

Davydenko changed racket models before the tournament and used the same racket in all six matches.

"I have only one racket," he said. "Surprising I didn't break a string. Warm up and play match, warm up and play match, every match, and I finish with the racket.

"I'm going to keep forever this racket."

Hitting serves at up to 132 mph, the 5-foot-10 Davydenko won five service games at love. He totaled 19 winners and had only 12 unforced errors, and his penetrating groundstrokes to the corners repeatedly made Nadal hit shots late and wide.

Davydenko also won 17 points at the net.

"He's playing unbelievable tennis," the No. 2-seeded Nadal said. "I can't play better today, because he played at an unbelievable level."

Davydenko improved to 12-3 in ATP finals, matching Thomas Muster (44-11) for the best winning percentage in the Open era. He also won $590,000.

Nadal received $295,675.