Promotion chasing Rovers have now taken just 11 points from their last 14 matches, but they remain just two points outside the play-off places.
Rovers, who had defender Tayo Edun sent off for two cautionable offences in the first-half, took the lead in the 77th minute, but wilted late on as Sammie Szmodics and Jack Marriott struck. Mowbray claimed Posh hadn’t looked like scoring in the second-half.
Mowbray told the Lancashire Telegraph: “Our supporters were excellent. They travelled a long way and they deserve better than that.
“We should have been attacking that goal second half, peppering their goal, but we had the sending half just before half time and it became more difficult.
“Then to get 1-0 up with 10 minutes to go, after they didn’t look like scoring. and it became a really frustrating day.
“We need to show more mettle, more knowhow and more nous when we are defending.
“We’ve had a lot of plaudits for our defending, but I find it hard how Peterborough managed to score twice in the last 10 minutes against us. We have to be better than that.”