Federer, who has won the Basel title five times and is the defending champion, ousted Mathieu 7-5, 6-4 and secured a spot in the finals opposite Juan Martin del Potro.
Del Potro cruised into the finals with a 6-2, 6-2 victory over third-seeded Richard Gasquet of France. The Argentine broke Gasquet's serve five times and wrapped up the victory in 67 minutes.
Federer needed 90 minutes to dispatch the French wild card, breaking serve twice and fired 10 aces to Mathieu's two.
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