Fuentes, a speedy outfielder, hit .218 with a .301 on-base percentage with Double-A San Antonio last season.
"I wouldn't say 2012 was a lost year, but it was a year of learning," said Fuentes, 22. "I think it opened my eyes."
This season has seen Fuentes -- one of four players the Padres obtained from the Red Sox in the Adrian Gonzalez trade in December of 2010 -- get back on the organization's radar in a big way.
Fuentes was added to the 25-man roster before Monday's game against the D-backs and was in the starting lineup in center field, hitting seventh.
Outfielder Jaff Decker was optioned to Triple-A Tucson after hitting .154 in 13 games with one home run and two RBIs.
Fuentes arrives with some big offensive credentials. He hit a combined .330 with 35 stolen bases and a .413 on-base percentage in 107 games, 93 with San Antonio and, most recently, 14 with Triple-A Tucson.
"This year has been awesome," said the left-handed hitting Fuentes, the cousin of Cardinals' outfielder Carlos Beltran.
Fuentes worked closely with San Antonio hitting coach Jacque Jones on his swing in Spring Training and continued that work into the regular season. Jones, who played 10 seasons in the big leagues, was very impressed with Fuentes.
"It's been just having a plan and using the whole field … opening the field for him and also not wanting to pull everything," Jones said. "We have worked on letting the ball get deeper on him and getting his [right] foot down early, which has given him a better chance to react. He's got the ability to drive the ball to the off-field gap."
Now, he'll get a chance to show what he can do at the Major League level.
"We'll see moving forward … but he'll get his starts," said Padres manager Bud Black. "It got to the point where [general manager Josh Byrnes and assistant general manager A.J. Hinch] felt the time was now to pull the trigger to see what he can do."