Wallace on Friday was called up from Triple-A El Paso to be a left-handed bat off the Padres bench. Wallace, who plays both first and third, was hitting .305 with eight home runs and 37 RBIs with the Chihuahuas.
The Padres optioned right-handed reliever Cory Mazzoni to El Paso and designated for assignment left-hander Eury De La Rosa to make room on the 25- and 40-man rosters for Wallace, a former first-round pick.
"He did his work down in El Paso and went after it the right way," said Murphy, who managed Wallace at Arizona State from 2006-08 as well as this season in El Paso until Murphy was promoted to interim manager of the Padres.
"Obviously playing for him early in my career, he was very influential and taught me a lot," Wallace said. "Already getting a chance to play for him again earlier this year allowed me to get back to some of the basics I want to."
Wallace, 28, is a .304 hitter in 650 Minor League games but just a .242 hitter in 311 games in the Majors, where he last played in 2013 with the Astros. Wallace was traded three times -- from St. Louis to Oakland, then to Toronto and finally to Houston -- between 2009 and 2010.
"He was as clutch a player as there was in the Pac-10 -- was it the Pac-10 back then? -- and seeing him again this season I saw a lot of the same things," Murphy said. "I think he's ready. I think letting him sit there [in Triple-A] for two months was good."