After three years with Portsmouth Rovers, he was signed by Football League Third Division North side Nelson at the start of the 1927–28 season.
[1] He spent most of the campaign as backup for regular goalkeeper Sam Warhurst, but eventually made his league debut for the club on 17 March 1928 in an away match against Hartlepools United.
[2] Warhurst returned to the starting line-up for the following game, and Mangham reverted to his regular place in the reserve team.
Nelson were beaten 1–6, the team's heaviest defeat for seven months,[2] and he was replaced by new signing Lewis Botto for the next match against Crewe Alexandra.
[3] Mangham did not play another first team match for Nelson, and his contract was subsequently cancelled in November 1929 as the club already had three more senior goalkeepers on their books.