The German side dominated from the kickoff as a shot from distance from Franck Ribery was parried by Plzen keeper Matus Kozacik but only into the path of Mario Mandzukic, who somehow managed to miss the target from yards out with a headed effort.
However, Pep Guardiola's side did take the lead in the 25th minute from the penalty spot as Robben was brought down in the area by a clumsy tackle from Roman Hubnik. Ribery made no mistake from the spot, slotting his shot into the bottom corner.
Kozacik kept Bayern from doubling their lead when Daniel van Buyten powered a header at goal but the keeper managed to keep it out with a one-handed save. That only delayed the inevitable as Alaba got his side's second, cutting in on his right foot and he curled a shot into the bottom corner.
It should have been three just before the break but Robben couldn't find the net as Kozacik denied his powerful left-footed shot with a good dive and he managed to beat the ball away with his left hand.