The club recalled Decker, an outfielder, from Triple-A Tucson, for the first time in his career.
"It's a great feeling coming in here and being welcomed like that," Decker said of all the affection he received.
The 23-year old left-hander -- pronounced Jeff, and spelled like his uncle, who passed away in the military -- hit .240 this season in the Minors, with five homers and 20 RBIs.
Decker got 40 at-bats in Spring Training and had a batting average of .175 with one home run, five RBIs and 11 strikeouts, which he said could help him.
"Just getting used to big league pitching and being around the guys learning a lot," Decker said.
Decker got the call late Tuesday night around midnight. His dad, mom, sister and some friends all made the trip from Arizona for Wednesday's game against the Braves.
He replaces outfielder Cameron Maybin, who was placed on the 15-day disabled list on Wednesday. However, Maybin is expected to miss a minimum of six weeks after he tore the posterior cruciate ligament in his left knee on Sunday.
"We needed an outfielder, and I think it was time-related with Tucson being in Fresno [on Tuesday] and what we found out about Cam," said Padres manager Bud Black. "He [Decker] can play defense and give us another player on the bench. Without Cam, we were down to a four-man bench."
Maybin was hitting .157 with one home run and five RBIs in 51 at-bats this season, and had previously missed 45 games with a right wrist impingement.
"It's frustrating for Cam," Black said. "Out of the chute, he didn't get off to a good start and then the wrist was a problem. Then he was finally starting to feel better where he was physically. He was ready to get into his season. This has been a tough first half for Cam."