Danny Wilson was less than impressed despite seeing his Sheffield United side book their place in the FA Cup second round.
David Clarkson fired hosts Bristol Rovers into a sixth-minute lead, driving at a back-pedalling United defence before planting a right-footed shot past George Long from the edge of the box.
The visitors equalised eight minutes after the break when Nick Blackman produced a superb left-footed finish from a narrow angle after running on to Porter's throughball. Chris Porter fired home a 62nd-minute winner before the Blades passed up chances to stretch their advantage.
"We were way below the standards we set in the first half and I can't put my finger on why because our preparation for the game was good," Wilson said.
"It wasn't like a cup tie in the first half. With all due respect, Clarkson will never score an easier goal because he ran at us unchallenged,
"The result is everything on days like this and we stood our ground in the second half. Blackman produced a great finish and Porter deserved his goal for his contribution."