Davydenko gave 12th-seeded Raonic all he could handle in the first career meeting between the players. The 22-year-old from Thornhill, Ont., finally put the Russian veteran away on his second match point in a second-set tiebreaker.
"I didn't play my best but I got through," Raonic said after serving only six aces in a match lasting just over 90 minutes. "I had to make the most of my game.
"I didn't serve that well but I still managed to take care of my serve. Late in both sets I stepped up my return game. I just made it through."
Also Monday, Ottawa's Jesse Levine lost in his opener against Kevin Anderson 6-2, 6-2 in 53 minutes a the South African dominated with 11 aces and four breaks of serve.
Raonic is playing his third spring event on clay after winning a round in Monte Carlo and advancing the Barcelona semifinals, where he lost to Rafael Nadal in heavy, wet conditions. He's trying to get his clay-court game ready for the French Open, which starts May 26. Raonic reached the third round of the Grand Slam event in 2012.
The 22-year-old Raonic needed 47 minutes to get through the opening set against Davydenko. The former World No. 3 saved a set point in the final game before Raonic popped a forehand winner deep into the corner to secure the lead.
"Davydenko's has been around and knows how to win," Raonic said. "He has a lot of experience — which I don't have — and that gives him something extra."
He finally put the game away in a second-set tiebreaker, scoring on a forehand deep into the corner on second match point.
Raonic's next opponent will be Madrid local Fernando Verdasco, who knocked Rafael Nadal out of the tournament a year ago in the third round when it was played on the controversial blue clay.
The pair stand level at two wins each in their career series, with Verdasco taking the last two — on clay — in 2011 at Estoril, Portugal and Rome.
"It's been two years since we played and I think I'm a better clay player than I was back then," Raonic said. "But the first thing is that I must play better than I did today. That's a key part to everything."