Rovers lacked any invention as they fell to a second straight defeat, managing just one effort on target over 90 minutes
Neither side created any chances of note during a low-key first half before Walsall took the lead through Tom Knowles' close-range finish seven minutes after the restart.
Danny Johnson then robbed Ro-Shaun Williams of the ball before rounding Jonathan Mitchell and passing into an empty net to double their lead.
Walsall move into the play-offs, while Doncaster drop to eleventh.
Scroll down for our player ratings.
1. Jonathan Mitchell - 6
Left with little chance with either goal, let down by some poor defending. Photo: Pete Norton
2. Kyle Knoyle - 5
Looked a shadow of himself after some exceptional performances last month. Saw a late effort blocked by Walsall net-minder Owen Evans. Photo: Liam Ford/AHPIX LTD
3. James Maxwell - 5
Defensively OK but offered nothing going forward. Photo: Howard Roe/ahpix.com
4. Tommy Rowe - 6
Held his own defensively. Looked to get forward from left centre-back but unable to exert himself in the attacking third. Photo: HOWARD ROE