Tsonga delighted his French fans in Metz with a 6-0, 3-6, 6-4 victory over Davydenko of Russia, and the fifth-seeded Seppi topped Frenchman Gael Monfils, the seventh seed, 3-6, 6-1, 6-4.
Monfils made it to the semifinals after sitting out the summer with a knee injury. He took the first set but Seppi saved five of six break-points to claim the victory.
Tsonga had lost the last two meetings with Davydenko but was able to break the Russian's serve in the ninth game of Saturday's final set to advance to the finals.
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