Manning was wide of the mark in the 17th minute but made amends three minutes later and then the best move of the game arrived when Niall Ronan linked superbly with Doug Howlett who set Barry Murphy free, his inside pass spilled by Lifeimi Mafi with the try line in sight.
Munster continued to press, Denis Hurley picking off Manning's delightful chip ahead and when Munster subsequently attacked off a middle of the field ruck, created by an impressive Damien Varley drive, Toby Morland's superb cut-out pass sent Hurley scampering over in the corner.
Manning converted then missed a penalty and then they reduced to 14 again with the harsh dismissal of Donnacha Ryan.
Munster continued to press but were caught when Llanelli broke out of their 22 for a length of the field try scored by Deacon Manu.
Munster: Felix Jones; Doug Howlett, Barry Murphy, Lifeimi Mafi, Denis Hurley; Jeremy Manning, Toby Morland; Julien Brugnaut, Damien Varley, John Hayes; Donnacha Ryan, Mick O'Driscoll capt; Alan Quinlan, Niall Ronan, Denis Leamy. Replacements: Denis Fogarty, Tony Buckley, Billy Holland, Tommy O'Donnell, Tomas O'Leary, Scott Deasy, Tom Gleeson.
Scarlets: Daniel Evans; Sean Lamont, Gareth Maule, Jonathan Davies, Mark Jones capt; Rhys Priestland, Martin Roberts; Iestyn Thomas, Ken Owens, Deacon Manu; Lou Reed, Dominic Day; Simon Easterby, Dafydd Jones, David Lyons. Replacements: Phil John, Emyr Phillips, Vernon Cooper, Richie Pugh, Lee Williams, Dan Newton, Rob Higgitt.