Gasol keyed the decisive period, during which the Grizzlies outscored the Thunder 22-15 and then held on down the stretch.
The center also grabbed nine rebounds and dished off four assists for the fifth-seeded Grizzlies, who retained home court advantage over No. 2 Oklahoma City in their best-of-seven Western Conference semifinal series.
The Grizzlies used a tough defense to limit Thunder star Kevin Durant to 25 points on 9-of-19 shooting. Durant also hauled down 11 rebounds and distributed five assists.
Reggie Jackson donated 16 points and 10 rebounds in the loss.