As a result, Chavez will fill the DH role most days of the week while Daric Barton mans first base, manager Bob Geren confirmed minutes later.
"Basically we're going to give Eric a chance to be the DH," Geren said. "In general, I feel like his best chance to help us is offensively."
The transaction, which came in the middle of several other roster moves following the team's final exhibition game Saturday, left Cust nearly speechless at his locker -- the same one he's occupied with the A's for the last three years.
"I was pretty surprised, but I've been playing this game long enough to know anything can happen," he said. "I don't have much to say right now."
Cust's spot on the 40-man roster was given to a surprising bullpen choice in Tyson Ross, who hasn't pitched above the Double-A level but is expected to lend a hand to a rather depleted A's bullpen.
Meanwhile, the A's have 10 days to make a move with Cust, who can be traded, released or put on waivers and, subsequently, be outrighted to the Minors.
The latter option is what not only Cust, but Geren and general manager Billy Beane, hopes evolves out of the situation.
"I'll probably stick around," Cust said. "There's not much out there right now, so there's a good chance I'll [clear waivers]."
Said Beane: "If for some reason he clears waivers and accepts the Minor League assignment, he'll get the at-bats he needs."
Cust received plenty of at-bats with the A's over the last three seasons, in which he led the team in home runs, walks and strikeouts each year. He tested the free-agent market following the 2009 season when Oakland decided to non-tender his contract, but he ultimately ended up back in green and gold with a $2.65 million contract.
Cust most recently posted a .240 average with 25 home runs and 70 RBIs to go along with a .356 on-base percentage in 513 at-bats through 149 games last year. He hit 33 homers in 2008 and 26 in 2007 while representing the A's most prolific power hitter.
Now the A's will rely on Chavez, who has appeared in just 121 games over the last three seasons, to provide some much-needed pop to an otherwise lackluster lineup.
"In fairness, you try not to use Spring Training as the judge," Beane said, "but Jack struggled all spring, so in some respect this gives him a chance to get going and also gives us the opportunity to see if Eric can shake off the rust and physically handle the position."
It's unclear whether Chavez and his surgically repaired shoulders and back will hold up in the batter's box on a daily basis, but that's something both Beane and Geren are willing to "find out."
"If you really just focus on having Eric and Jack there, having two people share the position that both needed at-bats, it didn't make much sense to go that way," Beane said. "We didn't think it was going to benefit the team or either player to be switching it up like that.
"There really wasn't any clarity up until today, and this is the best way for us to get some clarity."