Derby inflicted more misery on Millwall with a resounding win that lifted them up to third in the Championship.
Craig Bryson's first Pride Park goal set them on their way and Jeff Hendrick extended the lead before half-time.
Derby's leading scorer Steven Davies added a third after the interval following good work from Jamie Ward.
The result leaves Millwall without a victory in six league matches and they have gone 505 minutes without scoring a Championship goal.
The home side took the lead after 24 minutes, when Ben Davies cut the ball back from the byeline for Bryson, who scored from 12 yards out.
The finisher then turned provider, passing from the right-hand side of the area for Hendrick to finish clinically.
Steve Davies grabbed his fourth goal of the season after the interval, slotting in Ward's pass from 12 yards out.