World number one Roger Federer [Images] won his first title of the season at the Estoril Open on Sunday after Russia's [Images] Nikolay Davydenko retired with a leg injury.

The Swiss top seed saved a set point before winning the opener 7-6 and was 2-1 down in the second when number two seed Davydenko announced his decision to retire.

"This is not the way you want to win a tournament but that's the way it goes sometimes," said Federer, who recently hired clay court expert Jose Higueras to help him recover from the worst start to a season since 2000.

"It's great to win a title again in my first clay court tournament this season and it gives me great confidence for the Monte Carlo Open."

The 12-times Grand Slam winner has a perfect 10-0 record against Davydenko.

"I'm sorry about what happened today," Davydenko told a packed stadium in centre court at the Estoril Open. He later told reporters he planned to play in the prestigious Monte Carlo Masters Series next week.

"You know, I have some leg injury and I can't finish the match," Davydenko, a winner in Estoril in 2003, said. "Sorry guys."

In the women's final, second-seeded Russian Maria Kirilenko won her third career title, beating 2004 Estoril Open finalist Iveta Benesova of the Czech Republic 6-4, 6-2 in a rain-interrupted match.