Plus they dropped Conor Boylan and Tommy Grimes to reddish card dismissals within minutes of their second-half starting.
But they appeared motivated by the challenge and turned on the style to succeed their ease with second-half goals from Kevin Downes and Shane Dowling sealing the deal.
The win propels Shane O’Neill’s side throughout to the next month’s All-Ireland decider against Cuala or Liam Mellows, although Boylan and Grimes will both be suspended following the dismissals.
Limerick’s Ronan Lynch top scored for Na Piarsaigh with 14 points, 11 from placed balls, while Mike Casey headed a strong defensive display from the second-half and Dowling amazed when caused.
Slaughtneil came to the Donnycarney place armed using a outspoken support who participated in approval as their team controlled the first-half.
Captain Christopher McKaigue started the scoring after two minutes and Slaughtneil stayed in rod for the most part.
O’Doherty fired two points prior to renovating a 16th minute goal for Slaughtneil out of a punishment that put clear daylight between the groups.
Dual ace Brendan Rodgers has been hauled down from full-back Casey and O’Doherty slammed the resulting penalty to the roof of the net.
Boylan responded with a Na Piarsaigh goal six minutes later when he got home under pressure in the left, levelling it in 1-04 apiece.
However, the Slaughtneil answer was strong, and indicative of their enthusiastic approach, as they reeled off 1-01 from the following 90 seconds.
Meehaul McGrath thundered over a stage before Rodgers this time set up Brian Cassidy for a goal with a wonderful catch.
Slaughtneil deservedly directed by 2-06 to 0-06 in half-time and were making a mockery of the 11-point handicap placed on Na Piarsaigh from bookmakers.
Na Piarsaigh were under serious pressure as Slaughtneil also went for another goal just before the break when Rodgers was thwarted and hit nine wides in the half an hour.
The Limerick outfit reacted by drafting from the match again Dowling in half-time for his first appearance since the county final in October.
But they were remarkably reduced to 13 men by the 35th minute following the dismissals of goalscorer Boylan and wing-back Grimes, both for striking offences.
That left Slaughtneil with the larger numbers but Na Piarsaigh, seemingly sparked into life from the declines, stormed apparent on the scoreboard.
Lynch transformed a series of frees before Dowling fed up Downes for a 41st minute goal that place Na Piarsaigh 2-11 to 2-06 clear.
They were never in trouble then as they defence improved and closed Slaughtneil out with Lynch continuing to fire the frees.
Na Piarsaigh’s third goal in Dowling was a beauty, putting them seven obvious, as he gained back and flicked up the ball before volleying it home to the awe of the audience.
Gerald Bradley clawed back a late goal for Slaughtneil but it was mere consolation at that stage.
Na Piarsaigh: Podge Kennedy; Niall Buckley, Mike Casey, Jerome Boylan; Alan Dempsey, Cathal King, Tommy Grimes; Ronan Lynch (0-14, 0-11f), William O’Donoghue; Conor Boylan (1-00), David Breen, David Dempsey; Peter Casey (0-01), Kevin Downes (1-00), Adrian Breen.
Subs: Kieran Kennedy for Grimes (bloodstream), Shane Dowling (1-00) for A Breen, Kevin Ryan for D Breen, Kennedy such as D Dempsey, Gordon Brown for Downes.