Stanley lost 3-0 at Gigg Lane. Shakers loan pair Anton Forrester and Jordan Sinnott came in for their first starts and both scoredin the first half, either side of a straight red card for visiting striker Danny Webber.
Substitute Marlon Jackson then netted late onto seal a first League Two win of the season for Bury and leave Beattie's boys still searching for their opening victory.
Beattie said: "We played well for the first 20 minutes but then lost concentration and showed some weakness in getting sucked in to the way Bury wanted to play.
"We were playing good football and creating chances so I had to ask why we stopped playing that way.
"We switched off for the two goals and with Danny getting sent off it was always going to be an uphill battle from then on.
"I didn't see it but some of the lads said that Danny did catch him, so the referee went by the letter of the law even though there was no intention to play the man.
"There were a few choice words at half-time, which was the first time I've had to do that, but I believe in the squad. I said that I wanted them to go back out and perform, and I think we can take positives from the second-half display with 10 men."