The A's put three players on the 15-day disabled list -- reliever Joey Devine (right elbow inflammation), infielder Mike Sweeney (left knee inflammation) and outfielder Ryan Sweeney (left toe contusion). Left-handed pitcher Lenny DiNardo and infielder Kevin Melillo were designated for assignment.
Veteran reliever Alan Embree said he hadn't seen this many moves involving his team in more than a decade.
"It's a lot of moves but it's exciting," A's manager Bob Geren said. "Especially with a couple of guys making their debut.
"These guys were with us all Spring Training. They'll fit in nicely."
It was an important day for all four players activated before Friday's game against the Rangers.
Gonzalez made his Major League debut in center field on Friday. He is the third player to make the big leagues out of the blockbuster offseason trade that sent Dan Haren to the Arizona Diamondbacks. Gonzalez joins starting pitchers Dana Eveland and Greg Smith as already making it to the Major Leagues.
"That's half the guys from that trade," Eveland said.
Gonzalez, the A's top prospect, immediately improves an A's outfield defense that had been struggling. He was batting .293 with four home runs and 25 RBIs for Triple-A Sacramento.
"Carlos is an exciting player," Geren said. "We'll get him in the lineup and see how he does. It's exciting with the reputation and talent he has."
Buck returned to the leadoff spot after getting off to a miserable start and then going on the DL with shin splints. He had 18 hits in his last 34 at-bats for Triple-A Sacramento. That after starting slowly on his rehab assignment and then being optioned to Triple-A instead of getting called up when the A's were in Texas earlier this month.
"The reports we got said he was hitting well to all fields," Geren said. "When he does that he's locked in."
Buck said he feels refreshed. He opened the season feeling the burden of replacing Nick Swisher (traded to the Chicago White Sox). That resulted in him batting .154 with no home runs and six RBIs in 15 games before he went on the DL.
"I was looked at as the guy with long hair and his style of play," Buck said. "I was next in line and there was a lot of pressure.
"For me, it's a brand new season. I wanted to get back up here. The outlook I have for myself is a lot better."
Ziegler, who at 28 was in his sixth Minor League season, brings the story of a pitcher who reinvented himself and put in a lot of time to earn his way into the Major Leagues.
He converted to throwing sidearm a few years back and the results have followed. He led the A's organization with 12 wins last year. He had eight saves and had not allowed a home run in 24 1/3 innings for Triple-A Sacramento.
Ziegler was having success against right- and left-handed batters. Right-handers had a .118 average against him and left-handers had a .257 average.
Zielger is doubtful to pitch in the late innings.
"I'd like to get his feet wet in an easier situation," Geren said.
Veteran reliever Calero finally returned after missing the final month of the 2007 season with a torn right rotator cuff.
He had a rough 2007 overall, appearing in 46 games and finishing the year with a 5.75 ERA. That's two runs higher than his previous career high ERA of 3.41 in 2006.
Calero was 1-1 with 4.00 ERA in eight games during a rehab assignment that started on May 10. He will fill an important role with Devine, who was 3-1 with a 0.23 ERA, going on the DL.
"He said his slider feels good," Geren said. "His velocity is back where it was."
As for the injured players, Geren said Devine, who pitched last on May 25, will not throw for a few days. "We want to be cautious with him," Geren said.
Geren said Ryan Sweeney should be ready when the 15 days are up. That might not be the case with Mike Sweeney, who played only 74 games last season because of right knee injury. Now he's dealing with problems with the left knee.
"We'll give him some time off and see how it reacts," Geren said.