Edinburgh coach Rob Moffat admitted Fraser McKenzie's second-half yellow card cost his team a desperately-needed Heineken Cup win against Castres Olympique.
The Scottish club had battled back to level the scores 9-9 at Stade Pierre Antoine when the second-row was ordered to the sin bin for a professional foul as Castres surged forward. Edinburgh were made to pay a heavy price for the mistake, capitalising on the extra man to seize control of the tie with two tries in the space of five minutes.
"The yellow card was absolutely crucial. We gave away a number of penalties which we can't afford to do but they scored both their tries when we were down to 14 men," said Moffat.
"Castres have a big pack, especially in the back row and I thought Chris Masoe was the main man for them. He really stood out because he's so strong as a ball-carrier and is a real nuisance at the breakdown, but I thought we defended very well.
"The biggest disappointment was that our lineout just didn't function and when you don't get your set-piece right, then it's going to be very difficult. That shows how the rest of our play was to be in with a shout at the end. If we had more first-phase possession then we would have won.
"We always knew it would be tough here as Castres have not lost at home this season so we did well to go so close. It was another one that got away.
"We should be able to sort out our discipline as well as the set-piece this week and hopefully get a win next weekend."