"Philadelphia was aggressive," Oakland assistant GM David Forst said. "They made it clear they needed a starting pitcher to help out, and we were able to get the deal done."
Blanton, 27, won 14 games last year but has underachieved in 2008, his fifth big league season. In 20 starts for Oakland, Blanton was 5-12 with a 4.96 ERA. He was Oakland's Opening Day starter in March against the Boston Red Sox in Tokyo.
The Athletics get second baseman Adrian Cardenas, pitcher Josh Outman and outfielder Matthew Spencer, all minor leaguers.
The Phillies have been looking for a starting pitcher in an effort to plug holes at the back end of their rotation.
"We've been attempting to upgrade our rotation, and we feel like we've done that," Phillies assistant general manager Mike Arbuckle said. "We think Joe is a very strong, competitive pitcher that has the mental makeup to pitch productively in a pennant race. He pitches a lot of innings and takes some burden off the bullpen."
A's general manager Billy Beane traded Blanton a week after
sending Rich Harden to the Chicago Cubs -- and that's with his team
very much in contention in the AL West, six games behind the
first-place Los Angeles Angels.
"We started this process last November or December, and we said that we wanted to build a foundation and put together a group of players who were going to be here for a long time and sort of recreate what we did here at the beginning of the decade," Forst said. "We've made no secret that we're trying to build a longtime winner. We're trying to build something that's going to last. We want to be the ones who are being chased. We don't want to be doing the chasing."
Forst added that this doesn't mean the A's are writing off 2008, saying: "'08 still has a chance to be a good year. Beyond that is what we've done all this for."
Listed at 6-foot-3 and 225 pounds, Blanton had been scheduled to pitch Friday night against New York at Yankee Stadium in Oakland's first game after the All-Star break. Forst said he had yet to discuss with manager Bob Geren who will fill Blanton's spot in the rotation. Gio Gonzalez, a candidate to be promoted, has been pitching well for Triple-A Sacramento.
All three players acquired by the A's will remain in the minors for now.
Cardenas was batting .309 with six triples and 16 stolen bases in 67 games for Class A Clearwater this season; he ranked seventh in the Florida State League in batting average. Spencer was hitting .249 with six home runs and 41 RBIs in 84 games with Clearwater; drafted by the Phillies in 2007, this is his first full professional season.
Outman was 5-4 with a 3.20 ERA and one save in 33 games, including five starts, for Double-A Reading.
Information from ESPN The Magazine senior writer Buster Olney and The Associated Press contributed to this report.