It was a good away point for MK Dons. Following two successive wins this draw again confirmed Danny Wilson's side are rapidly moving out of the danger zone.
Merson decided to keep faith with the side which won at Bristol City but it was a decision which was hardly justified on a miserable first-half performance.
Merson's clever prompting was clearly missed despite the Saddlers enjoying most of the play.
Daryl Taylor, a former Aston Villa youngster, displayed plenty of talent but there was no finishing power.
On-loan Andrew Surman, a match winner at Bristol City, was unable to make the same impact and as a result Jorge Leitao was often forced to battle alone up front.
MK Dons - battling to avoid relegation - played with growing confidence.
Izale McLeod often caught the eye when he made some darting runs into the heart of Walsall's defence.
Clive Platt was not so conspicuous on his return to Walsall against the Saddlers' central defensive partnership of Neil Emblen and Ian Roper.
Emblen was fortunate not to conceded a first-half penalty when he put in a late tackle on the swift moving McLeod.
It was Roper who came to Walsall's rescue early in the second period when he blocked out a Ben Chorley shot.
Walsall's frustration resulted in Merson sending on Matt Fryatt and himself in an attempt to inject some more positive play but it was all to no avail.
But the rapidly improving Dons maintained their resolute approach with Michel Pensee-Bilong a stalwart in their defence.
The Dons kept plugging away and a Dean Lewington free-kick was only just off target.
Walsall's best chance fell to Leitao but his snap-shot was brilliantly saved by goalkeeper Matt Baker.