Michael Mellon scored the only goal on his Oldham debut to sink Cambridge, finding the net for the side managed by his father Micky.
The on-loan Burnley forward struck what proved to be the matchwinner in the 21st minute, and Oldham held on through spells of Cambridge pressure to take the points.
A Family Affair Decides It
The decisive moment arrived in the 21st minute. Luke Hannant played in Jamie Robson, who pulled the ball back for Mellon to stroke home for the side managed by his dad.