In the night's other game, Aurelien Chedjou's goal off Wesley Sneijder's corner kick in the 64th minute gave Galatasaray a 1-1 tie against visiting Chelsea, which had gone ahead when Fernando Torres scored in the ninth minute.
Ronaldo's two goals gave him 11 in the Champions League this season and 34 in 34 games overall this season. With 61 Champions League goals in his career, Ronaldo moved one ahead of Ruud Van Nistelrooy for third place, trailing only Raul Gonzalez (71) and Lionel Messi (66).
Benzema scored in the 13th and 57th minutes, while Bale had goals in the 21st and 69th minutes. Ronaldo scored in the 52nd and 89th.
Schalke's Klaas-Jan Huntelaar had the most spectacular goal on a volley in the fourth minute of stoppage time.
Second legs of the total-goals series are March 18.