Marsh-Brown's goals, both fine finishes in the second half, eased the Glovers past their non-league hosts after a first period where many chances produced nothing but frustration.
First team manager Gary Johnson was true to his word from Saturday where he promised a strong lineup for the visit to Tatnam Farm. A side resembling his foremost team began the game and although Poole had the first chance, the visitors produced more of the first half entertainment.
The goal in Saturday's 1-1 draw at Hereford was scored by Ed Upson and the midfield maestro was almost at it again but shot wide after Lewis Young had set him up.
Then defender Byron Webster and Sam Foley both shot wide before at the other end, Marek Stech gathered at the second attempt after he had saved the initial shot with his legs.
Upson then headed over the last chance of the first half as the interval came with the two sides level at 0-0.
Webster then turned saviour at the other end when his challenge thwarted a Poole attacker early in the second period and sub Reuben Reid saw a header blocked at close range from a Young cross.
Rohan Ince also had a shot blocked even closer to the goal following good work from Reid but the Glovers were soon in front when Keanu Marsh-Brown, another second half sub, slotted home after a ball through from midfield.
And the former Oldham star then made it two minites later when he turned inside and lashed home from twenty yards leaving the Poole keeper helpless.
Reid then almost made it three late on when Marsh-Brown set him up but manager Johnson had to be satisfied with two goals, a clean sheet and the unbeaten pre-season record maintained.
Yeovil team - first half...
Marek Stech, Luke Ayling, Byron Webster, Richard Hinds, Jamie McAllister, Lewis Young, Rohan Ince, Ed Upson, Gavin Williams, Sam Foley, James Hayter.
Keanu Marsh-Brown, Reuben Reid, Aaron Racine, Nathan Ralph, Salifa Cisse, Will Agbo, Mitch Brundle plus two trialists.