St Albans City manager David Noble said the sending off of Shaun Jeffers was "needless" and cost them the derby against Hemel Hempstead Town.
Saints had taken the lead in the first half at Clarence Park through another Michael Clark goal but Jeffers was then booked for getting involved with the taking of a Hemel free-kick.
A second booking came on the hour after a foul and goals from Brandon Barzey and Tre Mitford inside the final 14 minutes gave the Tudors a 2-1 win.
Noble said: "It was the manner in which we lost the game that is the disappointing thing.
"Going down to 10 men doesn't help anyone but to get one of the bookings for needless kicking the ball away.
"You know the rules this season and you know they are tight on them.
"You are then running a [fine] line.
"Any big occasion, you have to keep 11 men on the pitch, it's really important and we've usually been good at that but it's cost us the game.
"For 30 minutes we were excellent, scored the goal, but the last 15 minutes of the first half they came right back into it and we couldn't look after the ball.
"It gives them a foothold if you keeping giving the ball to them.
"Half-time came at a good time for us but the second half was disappointing.
"It is not a happy changing room."
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here