Del Potro took nearly 3 hours to eliminate Tsonga 6-4, 6-7 (9-11), 6-3.
Del Potro, the No. 4 seed in the tournament, will face Frenchman Michael Llodra in Sunday's finals.
Llodra upended third-seeded Janko Tipsarevic 6-4, 7-6 (12-10) to reach the Marseille finals for the third time in four years. He won the title in 2010.
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