His second-half effort was enough to separate the sides and sink the Dons, who had to win in order to chase down second-placed Peterborough.
And despite having nothing to play for but pride, the Saddlers survived a barrage of late pressure to cling on.
It means rivals Peterborough are promoted in second place after their victory at Colchester and the Dons now face a nerve-wracking play-off campaign.
The best effort came from Ibehre as he took down a long ball and fired just wide from 25 yards.
The Dons just didn't threaten at all despite large periods of possession and also lost Sean O'Hanlon through an injury with Jude Stirling replacing him at the heart of the defence.
The second half saw both teams improve and Sam Baldock fired in an early free-kick that Clayton Ince held with ease.
Then from nowhere Walsall took the lead. Ibehre did well as he controlled the ball and then turned Stirling inside out before firing a low shot past Willy Gueret at his near post from 25 yards.
Immediately, the Dons went on the attack and Baldock had an angled shot well saved.
This would be a pattern that would go only to repeat itself as time and time again the big keeper was their to deny the home side.
Jason Puncheon was next the next to try his luck only for Ince to hold well.
Soon after, the little magician then put in a brilliant cross that had Baldock been an inch taller would have converted.
He was able to pick out Mark Wright though minutes after but the winger headed straight at the legs of Ince.
It looked like it just wasn't going to be there day.
The Dons, who had by now brought on big-hitters Aaron Wilbraham and Peter Leven, kept on plugging away.
And Leven hit an absolute thunderbolt from 35 yards but Ince superbly turned past the post.
Walsall for the most part were defending brilliantly as they didn't allow the Dons in behind them and on one occasion when they almost did, Anthony Gerrard took the legs of Baldock.
From the resulting free-kick, Baldock almost caught out Ince but he just kept out his low effort.
That turned out to be the last decent effort as a play-off campaign for the Dons is now just weeks away.