Switzerland's Roger Federer watches a bouncing ball during his ATP Qatar Open tennis tournament match against Latvia's Ernests Gulbis in Doha January 7, 2010. [Xinhua/Reuters Photo]

 World number one Roger Federer struggled over three sets, while number two Rafael Nadal had an easy sail as both reach the Qatar Open semi-finals on Thursday.

Federer survived a scare to down 21-year-old Latvian Ernests Gulbis winning 6-2, 4-6, 6-4 to set up showdown against Russian third seed Nikolay Davydenko who beat big-serving Croat Ivo Karlovic 7-6, 7-6.

 

Spain's Rafael Nadal serves to Potito Starace of Italy during the ATP Qatar Open tennis tournament in Doha January 6, 2010. [Xinhua/Reuters Photo]