For their part Munster were without their international contingent and gave debuts to Ben Martin, Tony Buckley and John O'Sullivan while Mick O'Driscoll was partnered by Academy player Donnacha Ryan in the second row.
Playing with the wind in the opening half Paul Burke kicked Munster ahead in the 11th minute with a sweetly struck 40 metre penalty and added a second after Northampton skipper Reihana took a neat off-load from Lamont to score wide on the right.
Reihana was on the mark again in the 31st minute to send the Saints in at half time with a 8-6 lead. By then unfortunately, Munster had lost Mike Mullins who was carried off with was has been diagnosed as an Achilles tendon injury that looks likely to rule him out for a lenghty period. Saints lock James Percival was also stretchered off but medical reports are that the injury is hopefully not too serious.
Munster regained the lead at the start of the second period when Mossie Lawlor - looking sharp on his return from injury - engineered good field position with a chip 'n chase to set up the try for Paul Devlin.
Burke converted but a piece of Spencer magic allowed Darren Fox score a try that Reihana converted and he showed the Saints meant business when he opted to kick a penalty three minutes later as the visitors tried to close out the game.
However Munster showing commendable commitment struck for their second try when Frank Murphy took a quick tap penalty and had Henderson on his shoulder in support and then they defended gallantly in the closing stages as Northampton threw everything into attck in their efforts to snatch victory.
Munster: Ben Martin; Paul Devlin Rob Henderson, Mike Mullins (Barry Murphy), Mossie Lawlor(Ian Dowling);
Paul Burke (Jeremy Manning), Mike Prendergast(Frank Murphy); Frank Roche (Eugene McGovern), Jerry Flannery (Denis Fogarty), Tony Buckley; Donnacha Ryan,
Mick O'Driscoll; John O'Sullivan, Johnny O'Connor, Stephen Keogh capt
Northampton Saints: Bruce Reihana capt; Sean Lamont, Jon Clarke, David Quinlan, Ben Cohen; Carlos Spencer, Mark Robinson; Tom Smith, Dylan Hartley, Brett Sturgess; Damien Browne, James Percival, Mark Easter, Darren Fox, Dan Browne.
Replacements (from): Dan Richmond, Chris Budgen, Matt Lord, Mark Soden, Ben Jones,
Seamus Mallon, John Rudd, Rhodri Davies, Andy Vilk, Alec Rae.