The Ireland number ten – who lost his international place to rising star Jonathan Sexton during the RBS 6 Nations – was the star of the show for Munster, kicking 13 to points to help turn around a half-time deficit.

Dented by the absence of Ireland captain Paul O’Connell, Munster started slowly, allowing a Jon Clarke try and three Stephen Myler penalties to hand Northampton a 16-13 lead as they aimed to repeat their pool victory from the teams’ opening match of the competition.

But Munster haven’t lost a Heineken Cup match at Thomond Park for more than three years and stormed back with second-half tries from Jean De Villiers and Doug Howlett to set up a last four showdown with French side Biarritz.

And Australian coach McGahan admitted O’Gara was at the heart of the comeback as the 2008 champions reached their ninth semi final in 11 years.

“We needed a big game from Ronan O’Gara because Northampton believed they could get a result here,” said the Australian coach.

“And I thought he controlled everything. He was at his best with his game management.

“We needed a big game, and we needed to draw on everything we had, and we did that. The heart and the spirit of the players were tremendous and that's what you need in big games to get the result.”