Federer finished runner-up in Rome in 2003 and 2006

The world number one came through 6-3 6-4 against the Spaniard, who won on clay in Valencia last month.

"I think it was a good performance," said Federer. "Nicolas is a good player, especially on clay, and the first round is always difficult."

James Blake, Tomas Berdych and Marcos Baghdatis were other winners, while Tommy Haas retired with an injury.

Cypriot Baghdatis had an impressive 6-2 6-3 win over 2004 Rome champion Carlos Moya and ninth seed James Blake eliminated Gael Monfils 7-6 (7-4) 6-3.

I have been to the final twice, so I feel like I've almost won it Roger Federer

Haas trailed Radek Stepanek of the Czech Republic 6-3 3-2 when the German pulled out with a right shoulder injury.

Frenchman Richard Gasquet saw off Fernando Verdasco 6-1 7-5, and former number one Marat Safin overcame a shaky start to beat American qualifier Amer Delic 2-6 6-3 6-4.

"He started pretty well and was hitting unbelievable winners on the lines - I couldn't get into the game," said Safin.

"But then I tried to make him run and play more. It was just a matter of time."

Second seed Nadal, the Rome champion for the past two years, begins the defence of his title on Wednesday against Italy's Daniele Bracciali.

The Spaniard is on a record run of 72 straight wins on clay and is the favourite to prevent Federer winning for the first time in Rome.

"I've played here many times and I have been to the final twice, so I feel like I've almost won it," said Federer.