Defending champions Munster had victory snatched from their grasp in injury time at the Cardiff City Stadium because of a 52 metre penalty from Blues wing Leigh Halfpenny.
That secured the home side a 13-12 victory, but it wasn't enough to take them into the top four and clinch a place in the Play-Offs. Munster's losing bonus point enabled them to finish a point clear of the Blues and set-up an all-Irish semi-final.
"It's always a tight clash between Munster and Leinster - they won by a point the last time we played and we are eager to go up there and get the result that means we can continue in this competition," said McGahan.
"Leinster have been the most consistent side this season, finishing on top, but we are defending a trophy. It was always our goal to get into the last four and now we have to go on from here.
"It comes down to one-off matches from here on in and both Leinster and ourselves will want to ensure we reach the final two weeks later.
"We are in a difficult place at this time with injuries. We lost three or four players going into this game, but we hope to have a few players back for what promises to be a great game in Dublin.
"Our first priority in Cardiff was to win the game but at 13-12 we got the bonus point we needed. I am delighted for the players.
"We weren't too worried about who we were going to play. We were just focused on what we were doing.
"It's a fantastic advertisement for the competition that it has gone to the last day and the last 10 minutes to decide who plays who in the semi-finals."
Leinster managed the double over their arch-rivals in the Magners League this season and also beat them in the semi-finals of the Heineken Cup in Dublin last year.
But the league leaders, who had to come from behind to put paid to Edinburgh's brave bid for inclusion in the final four before running out 35-28 victors at the RDS, have a few major injury worries ahead of the Play-Offs.
Leinster coach Michael Cheika admitted he was concerned about the shoulder injury picked up by his skipper and second row Leo Cullen.
"His injury didn't look great. He will need a scan as he has had some shoulder problems in the past," said Cheika.
But influential back row man Shane Jennings is expected to be fit to return for the battle of the Irish giants, while international centre Gordon D'Arcy also looks certain to be available despite his early departure against Edinburgh.
"This is finals footie we are looking at now. We didn't have a good day with the scrums in Toulouse, but I'm always confidant of our ability," admitted Cheika..
"It was not the same opponents but they are not a bad scrum either. The front five looked to take charge out there and that's what you need in finals. These are the guys we will look to lead next week and hopefully the week after."
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