SAN DIEGO -- The Padres parted ways with utilityman Eric Patterson on Thursday, as they designated him for assignment to make room for first baseman Anthony Rizzo on the 40-man roster.

Patterson, who was the player to be named later in the December deal that sent All-Star first baseman Adrian Gonzalez to Boston, was hitting .180 in 89 at-bats with a .272 on-base percentage. He had eight stolen bases and was caught twice.

At the time the Padres acquired Patterson, general manager Jed Hoyer felt as if the 28-year-old was a good bench option for a National League team, someone who could play second base, as well as the outfield.

Patterson had two errors in 10 games at second base, and couldn't find much time in the outfield.

The Padres will continue to use Alberto Gonzalez and Logan Forsythe at second base, as Orlando Hudson remains on the disabled list. Outfielder Will Venable, recalled earlier in the day from Triple-A Tucson, can offer speed off the bench.

Rizzo realizes dream as he joins Padres

SAN DIEGO -- The first conversation Padres manager Bud Black had on Thursday when he met with rookie first baseman Anthony Rizzo sounded much like the one he had with the 21-year-old in Spring Training.

"I told him, you're a talented young baseball player," Black said. "Don't feel as if you're here to impress me or the [coaching] staff. You have already impressed us. Just do your thing."

Rizzo was officially added to the Padres' roster before the start of a four-game series with the Nationals at PETCO Park. Better still, he was in the starting lineup and was slotted in the seventh spot in the order.

"It's awesome, it's a dream come true," said Rizzo, facing a room packed with television cameras and reporters. "Here we are."

Rizzo, who hit .365 with 16 home runs and 63 RBIs in 52 games with Triple-A Tucson, arrived in San Diego on Wednesday morning, where he had his sore left thumb and the bone bruise in his left hand looked at by team doctors.

The thumb and hand checked out fine, clearing the way for Rizzo to be added to the 25-man roster. He took the spot on the 25-man roster -- and, subsequently, the 40-man roster -- of utilityman Eric Patterson, who was designated for assignment.

After essentially having his way with Pacific Coast League pitching for two-plus months, Rizzo was asked on Thursday what his expectations were.

"Hit doubles, play good defense," Rizzo said. "Whatever situation I'm in ... hit doubles."

Rizzo didn't walk into a room full of strangers when he arrived at PETCO Park. He spent part of Spring Training in the Major League clubhouse and appearing in games during the six weeks the Padres were in Arizona.

Rizzo also participated in the team's first rookie development program in January held at PETCO Park, a nine-day camp designed to help ease the transition of the Minor League players to the Major League level.

"I know what to expect coming in," Rizzo said. "Except ... I got lost a little today coming here."

Gregerson placed on 15-day DL

SAN DIEGO -- Relief pitcher Luke Gregerson, a key component to the Padres' success in the bullpen, landed on the 15-day disabled list on Thursday with a strained left oblique.

The Padres recalled right-handed pitcher Evan Scriber from Triple-A Tucson to take Gregerson's place on the roster.

Gregerson, who is 2-1 with a 2.63 ERA in 30 games this season, suffered the injury as he was warming up in the bullpen during the seventh inning of Wednesday's 5-3 loss to the Rockies.

"About my fourth or fifth pitch in ... I just felt something grab right under my rib cage here on my left side. I thought it was a cramp, at first. I tried to throw one more, it felt exactly the same," Gregerson said.

San Diego bullpen coach Darrel Akerfelds saw Gregerson wince, and immediately had him stop throwing.

"He's like, 'You've got to shut it down, that could be an oblique and you don't want to make it worse than what it can be right now. You could turn a 10-day thing into a two-month thing,'" Gregerson said. "We hoped it would feel better today ... but it just feels like a really bad bruise, now."

Scribner was with the Padres earlier this season, appearing in six games and posting a 2.45 ERA in 11 innings of work. He was 0-2 with a 4.67 ERA and eight saves in nine chances with Tucson.

Venable recalled from Triple-A

SAN DIEGO -- Padres outfielder Will Venable found something in Triple-A Tucson over the past week, and it's something he lost more than a year ago.

"I haven't felt it in a long time, but it's my [swing], yeah," Venable said.

"I was messing with some stuff that felt good, and then found something about four days ago that felt right."

The Padres optioned Venable to Tucson on May 23, and after 14 Minor League games, he returned to San Diego on Thursday.

Venable hit .529, getting nine hits in 17 at-bats in his last four games -- with two doubles, one home run and six RBIs, while scoring five runs.

"He was hitting the ball with authority. Even some of the outs he made -- according to our people -- were hard-hit outs," Padres manager Bud Black said.

When Venable was optioned to Tucson, he was hitting .224.

Venable flew into San Diego on Thursday morning, and said he's ready to help in whatever way he can.

"No one wants to get sent down," Venable said. "I think that I needed to be sent down. I think that I needed this -- not just for these next couple of weeks, but for my career, just to find something that I'd been missing.

"I just know that I found my swing, and I'm going to be able to go out there and do my thing."

The Padres optioned outfielder Aaron Cunningham back to Tucson. He hit .167 in 12 at-bats for the Padres.