Two goals in three first-half minutes from Murray Wallace helped Millwall into the third round of the Carabao Cup as they came from behind to beat Cambridge 3-1 at The Den.
Tom Bradshaw almost opened the scoring early on for the Lions when his acrobatic effort clipped the crossbar.
Cambridge took the lead after 33 minutes as Ben Worman's free-kick found an unmarked George Williams and the U's captain glanced his header into the bottom-left corner.
Millwall equalised minutes later as Matt Smith played in Wallace down the left flank and he drove into the box and hit an unstoppable strike into the corner past Dimitar Mitov.
Wallace scored a second in the 41st minute as Cambridge failed to clear Bradshaw's corner. The ball pinballed around the six-yard box before it fell to Wallace, who poked in from point-blank range.
The Lions added a third in the 53rd minute after Connor Mahoney weaved inside the area and pulled the ball back for Smith who took a touch and fired in from six yards.
Wallace almost completed his hat-trick on the hour mark with a towering header at the back post that cannoned off the bar.
Cambridge pushed forward late on and Sam Smith went closest, forcing a fingertip save from George Long.
