Roger Federer came through a worrying second-set slump to beat Spain's David Ferrer 6-3 4-6 6-3 and reach the semi-finals of the Hamburg Masters on Friday.

The world No.1 was in dazzling form at the start of the quarter-final as he broke the Spanish 12th seed in his first and last service games.

He edged into a 4-2 lead in the second only to throw that commanding position away, losing his next two service games as he suddenly seemed unable to get his forehand on target.

The Swiss, who had never lost so much as a set in six previous meetings with Ferrer, pulled his service game together for the decider but with his opponent gaining in confidence he had few chances to break.

The turning point came when Federer, serving at 3-3 and 30-30, saw a scooped forehand hit the top of the net and dribble over. It brought a relieved smile from Federer, while Ferrer threw his racket down in frustration on the red clay.

Federer duly held and took a decisive 5-3 lead when he converted a fifth break point in Ferrer's next service game.

Federer will continue his preparation for the French Open, the only grand slam he has never won, with a semi-final against fourth seeded Serb Novak Djokovic or Spain's Carlos Moya.

The favourite Rafael Nadal will look to extend his clay-court winning streak to 80 matches when he takes on fifth seed Fernando Gonzalez of Chile. The reward for the winner of that match will be a semi-final against Nicolas Almagro or 16th seed Lleyton Hewitt.

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