"Just before I got to first base, I heard something pop," he said. "It's weird. I mean, I've never experienced anything like that before."
The veteran catcher, a 37-year-old who made his Major League debut in 1997, was placed on the 15-day disabled list with a strained right hamstring. The Padres designated pitcher Edwin Moreno for assignment to make room for Blanco's replacement, Jose Lobaton, from Triple-A Portland.
"This is really the first time I've had a problem with my legs in my career," Blanco said. "I wanted to stretch it out a little bit. I wanted to run, but I couldn't. I thought maybe it was a cramp."
Padres catcher Nick Hundley went on the 15-day disabled list June 19 with a small fracture in his left wrist. With Hundley not due back until after the All-Star break, Eliezer Alfonzo is suddenly the club's veteran catcher.
The Padres selected Alfonzo, 30, from Triple-A Portland on June 19. Alfonzo spent parts of three Major League seasons with the Giants, and the Padres signed him in November as Minor League free agent.
"Alfonzo has experience," Padres manager Bud Black said. "It was safe to say we felt good about him as our third guy [during Spring Training]."
Last year, the Padres lost their two Opening Day catchers, Josh Bard and Michael Barrett, to the disabled list at the same time.
The Padres purchased Hundley's contract from Portland on July 4 last season when they put Barrett on the disabled list.
"It's tough to lose a guy like Henry," Hundley said Sunday. "But at the same time, it's a situation where Lobaton can come up and show what he can do."
Lobaton, 24, spent the entire 2008 season with Double-A San Antonio. He was on the Padres' 40-man roster entering Spring Training and named the best defensive catcher in the Padres' system by Baseball America.
He has appeared in 39 games for Portland this season, holding a .241 batting average in 133 at-bats.
Hundley, 25, sat with Lobaton on the clubhouse sofa to help him review paperwork before Sunday's game against the Dodgers.
"There's a lot of info when you come in, like scouting reports," Hundley said. "I was just trying to simplify things for him."
Blanco, who said his pain had worsened Sunday, said he hadn't had a chance to speak with his replacement.
"I will try to help him as much as I can," he said.
Amy Brittain is an associate reporter with MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.