Tsonga outlasted Nadal 7-6 (7-2), 4-6, 6-3 in Group B, saving 5-of-7 break points.
Roger Federer also made the semifinals out of Group B, finishing off an unbeaten run through the group by defeating Mardy Fish 6-1, 3-6, 6-3.
Novak Djokovic, Tomas Berdych and David Ferrer are all still in the running to earn semifinal spots out of Group A.
Federer had already wrapped up a spot in the semifinals before his victory over Fish, having defeated both Tsonga and Nadal earlier in the tournament.
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