Decker, the Padres' 22nd-round pick in 2009 out of UCLA, has nearly 3,000 Minor League plate appearances. He's hit 154 home runs, including 21 this season with Triple-A El Paso.
Decker flew Sunday from El Paso, Texas, to his hometown of Los Angeles and was in baggage claim at LAX when Padres farm director Sam Geaney called.
"I started by saying, 'Is this a joke,' " Decker said by phone late Sunday.
"And then I just sat there. I couldn't believe it. To this moment, I can't believe it."
Decker said he had essentially reconciled with himself on the flight that he wouldn't get called up.
"There's been a lot of moments where I thought it wasn't going to happen," he said.
Decker has spent parts of the last four seasons in Triple-A. But he had never been on the team's 40-man roster and he'd never been in the big leagues -- before now.
Corey Brock is a reporter for MLB.com. Keep track of @FollowThePadres on Twitter and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.