Butler, the No. 11 prospect in the Padres organization, gave up just one hit in his outing and threw 21 of his 42 pitches for strikes.
The right-hander walked a trio of batters, but was able to make the pitches he needed to make and escaped jams when necessary.
Salt River had a chance to get on the board early as they loaded the bases in second, but wasn't able to get anyone across as Butler induced a ground ball double play.
Wednesday's start was another strong one for Butler, who is coming off the busiest season of his career.
Butler threw a career-high 64 2/3 innings across three levels in the Padres organization this season and has given up just the one run in six total innings across three outings in the fall.
Mets prospect Mickey Jannis, a knuckleballer, was also impressive, despite being stuck with the loss.
Jannis gave up one run on three hits in his five innings, throwing 40 of his 71 pitches for strikes.
However, Peoria was able to get to him in the second.
The Javelinas got on the board early when Atlanta prospect Connor Lien drove in Fernando Perez with a base hit to center.
In the sixth, Mariners No. 6 prospect Tyler O'Neill provided some insurance run with a solo homer -- his third home run of the Fall.
William Boor is a reporter for MLB.com. Follow him on Twitter at @wboor. This story was not subject to the approval of Major League Baseball or its clubs.