And with skipper Paul O'Connell making only his fourth appearance of the season in the RaboDirect PRO12, McGahan had the perfect man to lead the revolt.
Treviso had begun the season searching for a first win away from Italian soil, and having already tasted success at both Ravenhill and the Sportsground, they were optimistic of a third Irish victory.
But after pushing the reigning champions hard in the first half, trailing just 10-6 at the break, tries from Keith Earls and James Coughlan proved too much for the Italians to overcome.
And Munster were even able to pick up a valuable bonus point with winger Simon Zebo crossing for a fourth try late on.
It was Treviso who came out of the blocks the quicker with Kris Burton, the architect of last week's win over Aironi, slotting the first points after ten minutes.
Ronan O'Gara evened things up with a penalty of his own midway through the half before Niall Ronan dived over for the game's opening try five minutes later.
O'Gara added the conversion but missing a penalty shot soon after, with a second Burton penalty making it a four-point game at the interval.
The home side scored their second try ten minutes into the second half when Earls pushed his claim for the Ireland outside centre jersey in the absence of Brian O'Driscoll by going over, O'Gara's conversion making it 17-6.
Treviso responded immediately through Manoa Vosawai although Burton was this time off target with the conversion.
And with 17 minutes remaining Coughlan sealed the win with Munster's third try, O'Gara's conversion putting the home side out of sight.
Treviso had no answer and Zebo was then able to add the icing on the cake with his score closing the gap to the second-placed Ospreys to just a point in the RaboDirect PRO12 table.
|Munster Rugby Score Card|
|Benetton Treviso Score Card|