Sean Long was in inspirational form for Saints, scoring two tries and creating several more. The half-back also kicked six goals for a personal haul of 20 points.
Leigh, who have now lost their last four matches by more than 60 points, were powerless to stop a Saints side who led 32-0 by half-time.
The signs were ominous for the home side as Mike Bennett and Long scored tries in the first five minutes, and worse was to follow.
A break by Lee Gilmour from deep inside his own half opened up the Leigh defence and Paul Wellens was able to finish off from close range.
The impressive Long took centre stage as he skipped through a couple of challenges and sprinted 40 metres to score in the corner midway through the half.
Then it was time for Long to turn provider, sending Jamie Lyon clear who in turn found Darren Albert in support to complete a stunning 50-metre move.
Five minutes before the break Saints hooker Micky Higham, playing his first game following a three-month injury lay-off, went over for a try against his former club which Long converted to make it 32-0.
There was no respite for Leigh in the second half as the gulf in class between the top and bottom of Super League was clinically exposed.
James Roby raced 70 metres for an interception try within seconds of the restart and the tries kept coming from the rampant Saints.
Long put Paul Anderson through for a rare try before Willie Talau gave Ade Gardner an easy run to the line. Keiron Cunningham and James Graham scored within minutes of each other and even in the final quarter Saints continued to pile on the points.
Gardner grabbed a second before Maurie Sa�asavalu crossed to take Saints to the 70 mark.
The biggest cheer of the afternoon was reserved for Leigh centre Ben Cooper who broke his side�s duck with a well-made try seven minutes from time.
But Saints completed the rout with a second try for Anderson in the dying minutes. Jason Hooper added a third conversion from as many attempts while Jamie Lyon also kicked two goals.
Leigh: Wilshere, Owen, Jackson, Cooper, Maden, Forber, J. Duffy, Fleary, Mears, Marshall, Leafa, Stapleton, Coleman. Replacements: Sturm, Stevens, Maddocks, C. Hill.
St Helens: Wellens, Albert, Lyon, Talau, Gardner, Hooper, Long, Fozzard, Cunningham, P. Anderson, Gilmour, Bennett, Roby. Replacements: Hardman, Higham, Graham, Fa�asavalu.
Leigh: (0) 4. Tries: Cooper.
St Helens: (32) 78. Tries: Bennett, Long 2, Wellens, Albert, Higham, Roby, P. Anderson 2, Gardner 2, Cunningham, Graham, Fa'asavalu. Goals: Long 7, Lyon, Hooper 3.
Referee: Karl Kirkpatrick (Warrington)