Tranmere boss Ronnie Moore was happy to benefit from a loss of discipline from Walsall's Andy Butler.
Defender Butler felt he had been caught in the face by Rovers' Andy Robinson in the 62nd minute and when referee Mark Brown ignored it, the defender brought down the midfielder on the edge of the box.
Robinson picked himself up and lashed a superb free-kick into the roof of the net to give Tranmere a 1-0 win.
Moore said: "I just felt Butler lost his discipline, gave away a stupid free-kick and Andy scored with a fantastic free-kick.
"It was the right punishment for the centre-half losing his discipline."
Walsall had Lee Beevers dismissed for a second bookable offence late on.