Birmingham City manager Chris Hughton said the sending off of central defender Curtis Davies was the turning point as his side were beaten 1-0 at Cardiff City.
Kenny Miller scored for Cardiff after 68 minutes, just five minutes Birmingham had been reduced to 10 men following the dismissal of Davies who brought down Miller when clean through.
Up until that point both sides had struggled to create golden opportunities. But the red card changed the match in the home team's favour, and Cardiff dominated the majority of the final quarter.
Hughton insisted the dismissal of Davies was harsh, adding: "My first reaction was to look at Curtis and Curtis jumped up straight away from the incident and didn't feel anything because he touched the ball.
"I think there was enough doubt on the incident that you don't give a red card.
"Stephen Caldwell was in close proximity and I can't sit here and say there's definitely no incident, but there's enough doubt that you can't give a red card.
"The game very much hinged on two instances. Of course the sending off, but also I thought in the first half we coped very well with a very real threat in Miller and I was confident we could cope with it in the second half again.
"The sending-off does change things but we can't make the kind of mistakes that we made and expect not to get punished."