OAKLAND, Calif. -- Kevin Towers sees an opportunity for the Arizona Diamondbacks to defend their division title, and he isn't about to sit still.

The NL West champion D-backs added a front-line starter Friday and boosted their bullpen, acquiring pitchers Trevor Cahill, Craig Breslow and cash from the Oakland Athletics. And Towers isn't done -- he still hopes to add another starter, though it's unclear if that will be Joe Saunders with the sides still far apart in negotiations.

The A's received starting pitcher Jarrod Parker, outfielder Collin Cowgill and reliever Ryan Cook in the trade Friday, all players the A's envision could be on the major league roster in 2012.

Towers has been committed to winning with pitching since he took the job as Arizona's general manager, and it paid off in his first season. Cahill will complement a talented rotation featuring 21-game winner Ian Kennedy and 16-game winner Daniel Hudson. Arizona won 94 games -- 29 more than in 2010 -- under manager Kirk Gibson on the way to a surprising division title over the 2010 World Series champion San Francisco Giants.

"We see a window after winning the NL West. We're in a go-for-it mode to stay on top of the division," Towers said. "We feel we've got a young starter to go along with Daniel Hudson, Josh Collmenter and Ian Kennedy. Hopefully, we can keep this rotation together for a long time. We've got four starters we feel are as good as anybody in the NL West. With Trevor in the fold we feel our rotation is that much better."

The Diamondbacks lost in the first round of the playoffs to Milwaukee in five games and are determined to get back in 2012.

A's GM Billy Beane, meanwhile, is in rebuilding mode with the hopes that the club will be able to build a new ballpark in San Jose and move out of the rundown Oakland Coliseum in a few years.

"These are two different organizations going in two different directions," Breslow said. "I'm excited to be on this end of this one, with a team competing for a World Series championship."

Cahill, who in April was rewarded with a five-year contract worth $30.5 million, went 12-14 with a 4.16 ERA in a team-high 34 starts. His deal from the A's took him through all three of his arbitration-eligible seasons and first potential year of free agency.