World number one Roger Federer [ Images ] advanced to the semi-finals of the Halle Open on Friday with a 6-4, 6-4 victory over fifth seed Marco Baghdatis of Cyprus.

Federer, four times winner of the grass tournament that serves as a tune-up for Wimbledon [ Images ], extended his winning streak on grass to 57.

• Paes-Dlouhy in Weber Open final

The five-times Wimbledon champion had skipped the German tournament 12 months ago but his smooth progress this week would have healed some wounds after he was crushed by Rafael Nadal [ Images ] in the French Open [ Images ] final on Sunday.

Federer will face Germany's [ Images ] Nicolas Kiefer [ Images ] in the semi-finals on Saturday.

Kiefer booked his place in the last four after France's [ Images ] Michael Llodra retired just 19 minutes into their quarter-final contest with a left arm injury. Kiefer was leading 4-0 when Llodra quit.