The A's have been interested in the 25-year-old Dominguez at least since last Sept. 25, when he picked up a win at Oakland, limiting the A's to two runs on eight hits in 7 1/3 innings while fanning three and walking none.
"He pitched against us the other day and struggled with his command, but he pitched against us in September and he was pretty much lights-out," manager Ken Macha said. "He's got a power arm, a plus-fastball and a plus-changeup."
Dominguez's Cactus League record this year -- 1-2, 8.44 ERA -- doesn't exactly shine, but the A's are impressed with his command of the strike zone.
While up with the Rangers last year, Dominguez made 10 starts in 22 appearances and went 4-6 with a 4.22 ERA. His Major League totals include 72 strikeouts, 42 walks and a 5-10 record in 109 2/3 innings over 32 games.
In contrast, Bynum's spring was phenomenal. He hit .373 with one homer and nine RBIs in 51 at-bats over 23 games, and stole six bases without being caught once.
In seven games with Oakland last year, Bynum collected two hits in seven at-bats (.286) and drove in a run.
With Triple-A Sacramento last year, Rheinecker, 26, went 4-0 with a 1.77 ERA before tearing a tendon in his left middle finger on May 13. This spring, he was 0-1 with a 4.,68 ERA in five games with the A's.
If things don't work out for the Cubs, Bynum may consider a fallback career as a journalist.
He scooped the world on his trade, spilling the beans before the A's were ready to announce the deal because not every player involved had been notified.
Then again, that the A's were looking to deal Bynum may have been the worst-kept secret in Arizona.
"I knew something was going to happen," Bynum said, "I knew if I didn't stay with the A's, I was going to be somewhere else.
"It's cool, I get a chance to go play and do what I want to do, play in the big leagues."
As happy as he is with his opportunity with the Cubs, Bynum is saddened to leave the only pro organization he's known. The A's made him their first choice in the 2000 draft (second round).
"Guys you play with, you become like family with them," Bynum said. "It's going to be hard, but hey, it comes along with the business."
That's why they could afford to lose him:
Bynum has experience as a middle infielder, but the A's on Friday unveiled an unusual choice to back up shortstop Bobby Crosby: the 6-foot-5, 275-pound Frank Thomas.
With no DH in effect for the game at AT&T Park, Macha wanted Thomas to get at least one plate appearance, so he listed Thomas at short and batted him third.
Thomas struck out to end the top half of the first inning, and Crosby replaced him in the bottom half.
Other scorecard oddities included an initial A's lineup card that listed both Milton Bradley and Jay Payton as playing center field.
Payton stayed in center while Macha decided to scratch Bradley, who has been nursing a strained quad muscle, because of the damp and chilly conditions.
Macha was hoping a few relievers, especially Huston Street and Jay Witasick, would get some work Friday and/or Saturday, but rain may wash out that opportunity.
An even greater concern is what happens at the beginning of next week, when the A's are supposed to open the regular season with three home games against the Yankees.
But the forecast currently calls for rain, and lots of it, for the home opener Monday.
Because the Yankees aren't scheduled to come to Oakland again this year, and the two teams have no compatible off-days when both teams are on the West Coast, any rainout would have to be made up with a split doubleheader Tuesday or Wednesday.
Both Forst and Macha said if that's the case, the A's could open the season with 12 pitchers on the roster, instead of 11, so that they would be covered for the doubleheader.
It's possible that Kirk Saarloos or Joe Kennedy could make an emergency start against the Yankees, but Forst said the newly acquired Dominguez will almost definitely begin the year in Sacramento.
"We'd like to see him pitch a little bit for us before we make that decision [to bring him up]," Forst said.
The A's get their first chance Saturday to play in two-thirds of the Coliseum (the upper deck has been closed off to create a more intimate setting for fans) when the Bay Bridge Series continues. Right-hander Esteban Loaiza will be matched against Giants right-hander Matt Cain.