United went into Saturday's third round tie at the City of Manchester Stadium hopeful of causing an upset, and lead through an early striker from Andy Keogh.
But Fowler, making his first City start of the season, scored three second-half goals to easy the Premiership side into the fourth round.
Laws said: "In the first hallf we were superb, deservedly 1-0 up and probably should have been 2-0.
Laws: Fowler was difference
"Stuart's aware that we went at them and matched them, second half in the first 15 minutes totally killed the game for us - they won the game in that 15 minute spell.
"They stepped the tempo up, and we gave the ball away a little bit cheaply.
"The penalty was harsh, he's been pulled down and landed on the ball."
Laws also singled out striker Fowler for praise, adding: "He is such an intelligent player, we were looking quite comfortable in the first-half and handling Robbie pretty well.
"I don't know why he has not been playing but he kept dropping into areas where our centre-halves did not want to be and we couldn't cope.
"We are a League One side and his knowledge and experience is bound to catch you out in the end."