But 10-man Dons, trailing to Lewis Grabban's debut goal for the Cherries, hit back to snatch a point through Daniel Powell's second-half equaliser.
Former Leeds and Manchester United midfielder Alan Smith was sent off in the 19th minute after appearing to miss-time a challenge on Cherries midfielder Harry Arter, who was replaced at half-time and his dismissal climaxed a chaotic short spell for the Dons, who fell behind to a close-range Grabban strike two minutes earlier.
Grabban's goal had an element of good fortune about it - Charlie Daniels appearing to miscue his pass into the path of the summer signing from Rotherham after rounding Adam Chicksen.
Daniels twice went close to increasing the lead as Bournemouth bossed the first half, but MK Dons improved dramatically after the break and got a 62nd-minute equaliser when Gary McKenzie set up Powell to score his second goal in consecutive matches.
Dons hung on as Lee Barnard had a goal ruled out for offside and Steve Cook hit the crossbar with a header as the visitors withstood heavy late pressure.