After the break Harriers stepped up a gear as they seemed to realise that Cambridge were offering no real threat and began to dominate the game completely.
After 61 minutes Andy Bishop almost opened the scoring when he raced clear of the United defence but Marshall got his fingertips to the shot and turned it out for a corner.
The opening goal came soon afterwards, however, JJ Melligan getting in the way of a poor clearance by Marshall and looping a header back over him. Minutes later it got even better for Harriers, a free kick on the left wing was floated towards the far post by Flynn and found Wes Morgan who rose unmarked to head past Marshall to double the lead.
Cambridge finally came out of their shell in the closing minutes as they tried to find a way back into the game. Ten minutes from the end a cross from the left found Luke Guttridge who headed over with Fraser Digby
flapping at thin air in the Harriers goal.
Shortly afterwards David Kitson got clear of the Harriers defence and beat Digby with his shot but saw it cleared off the line by Dion Scott.
Harriers never looked in any danger of losing their grip on the game and easily played out time to claim all three points.