Saracens coach Mark McCall was mightily relieved after his side reached their second straight Heineken Cup semi-final with a 17-15 win at Ravenhill, and acknowledged that the first-half dismissal of Ulster full-back Jared Payne was a game-changer.
The hosts were forced to play most of the game without Jared Payne, who was controversially sent off in the fourth minute after a shuddering tangle with Alex Goode which forced the Saracens full-back off the field.
Despite being down a man, Ulster refused to buckle and led 9-5 at the end of the first half but, after the home side lost key players Rory Best and Ruan Pienaar to injury, Sarries eventually got in front and held firm despite Ulster's storming finish which saw them narrow the visitors' lead to two points.
Tries in either half from Chris Ashton, along with one from second row Mouritz Botha, proved enough for McCall's men, with all of Ulster's points coming from the boots of Pienaar and Paddy Jackson.
"Ulster deserve an enormous amount of credit after losing a man after five minutes and, not only from the effort they put in, but to also be as tactically astute and aware as they were was a great achievement and we're just lucky we got over the line at the end," McCall said after guiding his team to a Twickenham date with Clermont.
"It definitely wasn't intentional (Payne's collision) but it was reckless. You could argue both ways, but it's a big call to make five minutes into the match and it changes the match.
"At times we played some good rugby and at times our physicality was outstanding, but we kept on showing unbelievable indiscipline.
"We gave away too many penalties and we kept them in the game and we kept the crowd in the game, and we were fortunate to get away with the win."
Ulster coach Mark Anscombe felt Payne should have been shown a yellow card, but praised his side for battling through with 14 men and running Saracens - who scored three tries - so close, with an Ulster win a possibility right up until the final play.
"When you lose a pretty important player five minutes into the game, you're always going to have your backs to the wall," Anscombe said.
"It's unfortunate. It was a collision in the air and did it warrant a red card? I think we're pretty hard done by there.
"Sometimes I think with these it's the emotion of the injury (that) creates the penalty, and I think at worst it was a yellow card. To have a red card four minutes into the game meant we were always going to be chasing our tails.
"I've got to take my hat off to the boys to hang in there and, to actually be taking the game to them and trailing 17-15 in the 80th minute, we've got to be really proud of their effort.
"Jared, the whole time, had his eyes on the ball. I mean, how's that a red card? I think that's the emotion of the injury," Anscombe added.
"You saw how difficult it was as, a couple of the tries they scored, we had numbers down. We went to the break at 9-5, which was a pretty good feat, and to keep it so close at the end... but that's the way it goes at times."