Boro were stunned by first-half goals from Jay Rodriguez, Wade Elliott and Michael Duff, and Andrew Taylor's late strike could not paper over the cracks.
"It was a free shot at three points for them," admitted Mowbray.
"They were always going to come at us strong at the start, but we weren't ready for it and that's the frustrating thing for me.
"It's an easy story to write - the team that wanted it more - but I'd like to think that's not the case.
"Two goals in as many minutes knocks the stuffing out of any team. That gave us a mountain to climb and it proved too much. The evidence was out there on the pitch."
Source: PA
Source: PA