The Merseysiders always looked comfortable but wasted some gilt-edged chances.
And it could have been a different outcome had home keeper John Achterberg not produced a superb fingertip save to keep out a powerful shot by Levi Reid in the 67th minute.
Danny Harrison and Stephen Jennings, who came into a changed home line-up, tested Vale keeper Mark Goodlad early on before Iain Hume wasted a good opportunity when set up by Paul Hall.
Then Hume brought a good response from Goodlad in the 29th minute after good work by Harrison.
Tranmere finally broke through in the 40th minute with an 11th goal of the season from Hall. He flicked the ball out of the reach of Goodlad from a headed pass by Hume following a Rovers goal-kick.
Hall wasted a good opportunity just after half-time. Ian Sharp headed over and then fired against the bar when set up by Ryan Taylor in the 66th minute.
Hume had no luck with two chances in the 74th minute and in the 88th minute home substitute David Beresford brought the best out of Goodlad with a powerfully struck free-kick.
Vale never threw in the towel, but Christian Hanson and Craig James both failed to test Achterberg with late free-kicks.
Hall was outstanding for Rovers, but there was also a terrific debut for teenage defender Carl Tremarco.