Davydenko posted a 6-4, 6-3 victory in just 76 minutes on a windy day for his first career claycourt championship.
The 21-year-old Davydenko, who ousted countryman and sixth seed Yevgeny Kafelnikov in the quarterfinals, improved to 13-10 on the year. He began 2003 with a hardcourt title in Adelaide.
After Adelaide, Davydenko's luck took a turn for the worse as he failed to advance past the quarterfinals in five straight tournaments and suffered a broken left wrist against Magnus Norman at Memphis in February.
While out for a month, he trained using only his forehand and quickened up the recovery. But his return in Miami resulted in a first-round defeat, followed by another in Russia's embarrassing 5-0 Davis Cup loss to Argentina.
"After my injury, I lose two matches, then I win a tournament. I got into the Top 50, so this is an important week for me," Davydenko said after collecting a check for $73,000.
The 26-year-old Calleri saved two match points before plowing a backhand into the net.
"I tried to make no mistakes and tried to force him to go for winners," said Davydenko, who warmed up indoors before battling the wind. "I didn't feel so great, and I couldn't think about winning. The first set was tough to play, but I don't know what happened in the second -- he seemed to have no concentration.
"I'm happy. Anytime you win a tournament, it's great."
On the women's side, eight matches in nine days caught up with German qualifier Julia Schruff as second-seeded Spaniard Magui Serna defended her title with a 6-4, 6-1 win in 67 minutes.
The 20-year-old Schruff had defied the odds to reach the final in only her fourth tournament at the WTA Tour level.
"My dream has ended for this week, but it will go on," Schruff said. "I was so very tired, it has been a tough week. In the third set I couldn't run at all due to a muscle pull. I'll take two days to sleep and then have a little party. Then it will be back to practice."