Cullen admits Leinster rode their luck and that he feared visitors' positivity and momentum
Leinster boss Leo Cullen admitted his side were "fortunate" to beat Ulster and book their place in the semi-finals of the Champions Cup.
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The champions will play Toulouse back at the Aviva in next month's semi-finals after third seeds Racing 92 surprisingly lost at home to their 14-man French rivals yesterday.
But there were a number of times throughout Saturday's absorbing 21-18 contest that Cullen worried his own side could have been making a similarly early exit to a local rival.
"You are always so wary about teams that are close and are building and building," he said.
"They have a lot of positive momentum there and they've had disappointing days.
"And everyone is talking about Leinster are going to win and it's just a matter of turning up.
"That's just not the way it actually works in reality.
"Then, you have a slow start in the game on top of that and you have to chase the game. It is always difficult.
"Any game when you are chasing it is tough going in Europe with the quality of teams that are there.
"Ulster have had to fight through a number of really tight games this year.
"That makes them very dangerous because they've been in that situation and the know what to do, how to manage the game.
"We're through to the next round. But, and it's a big but, we're pretty fortunate as well."
Despite the scare, Leinster have not lost a knock-out contest since 2017 and Cullen acknowledged that his side's big game experience stood to them in a tense final 15 minutes.
With nine minutes to go, Ross Byrne - playing in place of the injured Johnny Sexton -knocked over the winning penalty despite dealing with muscle tightness when deciding to go for the posts.
"You think back to the way the (last year's) quarter-final was against Saracens, who had a lot of guys coming back post-Six Nations and they had a mixed campaign," he said.
"We got off to a perfect start in that game, James (Lowe) makes the break up the sideline and we score, and we're into the game.
"They're having to play the catch up game and that's the way I was looking at it (this weekend. 'Jeez, Ulster have had the perfect start here and are we going to struggle today?'
"And it was a struggle but at least we were able to find some sort of a way to dig ourselves out of it.
"Obviously they missed a conversion which means that it is an even game at the end.
"We were running out of subs and that was the worrying part because if that game had have gone to extra-time we were in trouble because we didn't have many people. And if it went on after that then it was a place-kicking competition and Ross had just gone off, so it was a nervy period.
"Thankfully Ross kicks that goal with the cramp that he was flagging just before.
"There was lots of things going through my mind at the end but credit to the players for sticking at it when probably not being fully at their best."