Lampard, who had come on as a substitute for the injured Ramires, netted the second goal in first-half stoppage-time.
The England midfielder took his Chelsea career goal tally to 201 — within one of Bobby Tambling’s record — when he drove home a penalty after Leon Britton had fouled Juan Mata in the area.
That was enough to move Chelsea three points clear of fifth-placed Tottenham Hotspur in the race to qualify for the UEFA Champions League.
“We played good football,” Benitez said. “The idea was to score an early goal, we didn’t manage that, but we did eventually score and then pushed for the second before halftime.”