Ibehre had only been on the pitch for two minutes when he sent a fine header into the bottom corner from Luke Chadwick's pinpoint cross.
Exeter started well and went in front with their first attack after eight minutes. Jamie Cureton chested down Steve Tully's throw, turned quickly and sent an exquisite chip over the head of MK Dons goalkeeper David Martin and into the far corner from an acute angle.
Scott Golbourne shot straight at Martin after a neat one-two with David Noble, while the Dons had some decent chances of their own.
Michael McIndoe skied high after his initial shot had been blocked and Exeter goalkeeper Paul Jones made a brilliant save to deny Sam Baldock.
John O'Flynn rolled the ball wide for Exeter after being presented with a great chance by Golbourne and it proved costly as Ibehre levelled in the 73rd minute.