Derek McInnes' strikeforce were in top form as Steven Milne struck a brilliant opener and both Kenny Deuchar and Collin Samuel hit doubles.
New signings Danny Grainger and Filipe Morais helped create four goals between them as Stenhousemuir struggled to deal with crosses.
Murray Davidson and Dave Mackay also made competitive debuts in the comfortable first-round win at Ochilview.
There was a sense of early-season rustiness about the start of the game, with even the groundsman taking his time to get going by forgetting the corner flags.
After a short delay, which followed a minute's silence for former Stenhousemuir and Motherwell striker Paul McGrillen, Saints took a while to get into their stride on the artificial surface.
Milne had the first sight of goal in the 19th minute when he stretched to hook wide Liam Craig's free-kick but he lit up the contest three minutes later.
The striker collected the ball 20 yards and dipped a shot with the outside of his right boot over Chris McCluskey and into the top corner.
Stenny right-back Willie Lyle had gone down clutching his face in the build-up as Craig ran past him on the left wing and went off with a bloody nose moments later, with striker Scott Dalziel coming on.
Saints keeper Alan Main had to look lively to palm over crosses from Dalziel and Pat Scullion but the visitors moved two ahead in the 28th minute.
Deuchar laid the ball out to the right wing for Morais and met the resulting cross from six yards, guiding his header down and into the net.
Morais sliced wide from 12 yards after being played through by Milne, and Craig shot wide from a similar distance after Deuchar had laid off another Morais cross.
Stenny's best chance of the half came after Jordan Smith and Dalziel had headed on a corner but Iain Diack could not nod the ball on target from close range.
The Irn-Bru Second Division newcomers enjoyed a decent spell just after the interval with Main parrying powerful long-range efforts from Dalziel and Kevin Motion.
But St Johnstone stepped up a gear midway through the half.
Samuel, who replaced Milne early in the second period, dived to head home in the 67th minute after Deuchar had nodded a Morais cross across the face of goal.
Deuchar grabbed his second three minutes later. Grainger overhit a cross but Craig just managed to keep it in and head it back across goal for the former Gretna striker to hook home with McCluskey stranded.
The hitman turned provider for Samuel's second in the 75th minute when he nodded down Grainger's cross for the substitute to volley into the corner from 15 yards.
The Perth side now host Burnley next Saturday before beginning their SPL against Motherwell, whose assistant manager Peter Ward was among the spectators.