OAKLAND -- Big-time power prospect Matt Chapman joined the A's for Thursday's 8-7 win over the Yankees, signaling a big step in the continuation of a youth movement that will likely come to define Oakland's season.
"It's gotta be probably the best day of my life so far," Chapman said of his promotion to the big leagues.
Veteran infielder Trevor Plouffe, brought in as a free agent during the winter to serve as a stopgap at third base, was designated for assignment upon Chapman's promotion from Triple-A.
"He was excited to come here," A's general manager David Forst said of Plouffe. "Unfortunately it just didn't work out. It was one of a number of things that haven't gone the way we expected this early in the season. We're sorry to see Trevor go and wish him the best of luck, but we're obviously excited to have Matt here."

The changing of the guard wasn't expected so soon. But Plouffe was hitting just .214, while Chapman kept belting home runs -- he had 16 with the Nashville Sounds and was averaging one homer per 10.88 at-bats -- while continuing to flash his Gold Glove-caliber defense at third.
"It feels great.," said Chapman, ranked by MLB Pipeline as the A's No. 4 prospect. "I don't know if it all really hit me until I got to the field today and saw my jersey in the locker. Definitely a dream come true and just an honor to be a part of something like this."

Chapman drew the start at third base and hit seventh in the A's series-opening lineup against the Yankees, and the Cal State Fullerton product -- Oakland's first-round pick in 2014 -- said he left 23 tickets for friends and family members. Chapman finished 0-for-3 with a pair of walks, scoring a run in Oakland's 10-inning victory.
Afterward, he said of his first plate appearance, "Definitely a little nerve-wrecking. I guess I haven't felt jitters like that in the batter's box in a long time."
A's manager Bob Melvin was tasked with speaking to Plouffe during the team's return flight from Miami on Wednesday evening. Melvin has raved about Plouffe's leadership qualities since Day 1 of the infielder's brief tenure in Oakland; in just a few months, he became a mentor to young infielder Ryon Healy -- and Chapman.
"The first thing he said to me was how happy he was for Chapman," Melvin said, "so that tells you a little something about him."
A remodeling A's organization promises patience with its young squad, which also features rookies Chad Pinder and Jaycob Brugman. Top prospect Franklin Barreto is soon expected to arrive on the scene, likely when the A's can find a trade partner for second baseman Jed Lowrie.
"You look out on the field, it's obvious what's going on," Forst said. "It's obviously time for us to see some of these guys. We have some opportunity for these guys, and it's up to them to see what they do with it."
"That's the direction," Melvin said, "and this is a group of guys we kind of identified a couple years ago being a core group of guys that we feel like we can build around in the future, and now is that time."
Worth Noting
• Rehabbing shortstop Marcus Semien is scheduled to join the A's for batting practice on Friday for the first time since undergoing right wrist surgery. Semien remains on track to return from the DL in early July.
• Steve Scarsone, the A's traveling Minor League instructor, was on hand to assist Melvin while bench coach Mark Kotsay is away to tend to a family matter.