Rodriguez replaces catcher Eliezer Alfonzo, who was placed on the 15-day disabled list with a left knee sprain and could miss the rest of the season.
Alfonzo was injured during the 10th inning of Friday night's 5-3 loss to the Oakland Athletics after Donnie Murphy crashed into his knee trying to score on a grounder to first base.
Alfonzo made sure Murphy never got that far, hanging on to the ball before sprawling in the dirt.
Rodriguez knew something was up after his manager at Fresno, Dan Rohn, asked him where he'd be following Friday night's game.
"I went back to the hotel [in Las Vegas] and was in the restaurant when [Rohn] called me and said, 'You're going to the big leagues,' " Rodriguez said. "I wouldn't believe it. I thought he was joking at first."
He hasn't been to sleep since.
"I keep thinking about how excited I am," he said. "Last night I couldn't talk. I was babbling. I tried to explain to everyone how I felt. It was awesome."
Rodriguez finally found the words to tell his parents, his wife and his two children, all of whom are in Venezuela, that his dream was coming true.
"I never thought about giving up," he said. "I have a wife, family, mom and dad, even a sister that I need to support. I keep them in mind and keep working. When I see my friends go up, like Paul Lo Duca, after so many years in the Minors, I say, 'Why not? Why can't it happen to me?' "
Rodriguez was selected over Justin Knoedler, who has made brief appearances with the Giants in each of the past three years.
"[Rodriguez has] been in the organization for a while, and he knows the pitching staff from Spring Training," manager Bruce Bochy said. "He's been doing a good job."
Rodriguez, signed as a non-drafted free agent in 1995, looked around the clubhouse and began ticking off the names of players who had been his Minor League teammates.
"All these guys," he said. "I've played with pretty much everybody, everywhere, in the Minors."
The news isn't as good for Alfonzo, who arrived in the clubhouse on crutches. If he needs surgery, his season is over.
"We're looking at least two months," Bochy said. "If it's surgery, it would be the year. More than likely, it's the year. We're going to have to talk to [him] about that."
Outfielder Dave Roberts returned to his familiar spot at the top of the lineup after missing nearly a month following elbow surgery on May 11.
Roberts was recalled from his rehab assignment with the Grizzlies and activated from the disabled list, and he arrived at the ballpark less than two hours before game time.
He takes the place of outfielder Fred Lewis, who went on the 15-day DL with a right oblique strain. Lewis, who had originally replaced Roberts, underwent an MRI, with results due later in the day.
"Ideally, we wanted to give him a few more at-bats," Bochy said of Roberts. "We had to rush him a little, but he's fine and good to go."
Pedro Feliz never flinched when a reporter asked him jokingly what he thought of being in the starting lineup as a catcher.
"It doesn't surprise me," Feliz said. "I'm ready."
Feliz, the emergency backup to the emergency backup, donned Bengie Molina's equipment with two outs in the 10th on Friday and crouched behind the plate for the first time in organized baseball.
"Playing third base is not that easy, but it's tougher behind the plate," said Feliz. "I don't know how they do it."
As Alfonzo was being treated, it didn't occur to Feliz that he would be called upon to finish the inning.
"I was looking around, hoping he could get back up and do it," Feliz said.
Feliz has now played six of the nine positions, needing to play second base and center field, and pitch to get all nine.
Kevin Frandsen is the Giants' emergency catcher, and has caught bullpen sessions and worked behind the plate. But he was used as a pinch-hitter in the ninth inning, and was thus unavailable.
"That's the one concern when you have two catchers," Bochy said. "But I'd rather manage to win than manage with the fear of losing my catcher."
Right-hander Matt Cain (2-5, 3.54) gets the call for Sunday's series finale against A's left-hander Lenny DiNardo (2-2, 1.45). Cain leads the Giants with 58 strikeouts, though he leads the National League with 40 walks. One of his more memorable efforts was a one-hit shutout against the A's in Oakland last year.