The Arizona Diamondbacks have traded right- hander Ian Kennedy to the San Diego Padres for left-handed setup man Joe Thatcher and minor league pitcher Matt Stiles.

The Diamondbacks will also receive San Diego's competitive balance Round B selection in next year's MLB Draft

Kennedy enjoyed a breakout campaign in 2011, as he won 21 games, was named to his first All-Star Game and finished fourth in National League Cy Young Award voting.

However, it's been a different story for the former first-round pick this season.

After winning 15 games a season ago, Kennedy has been largely ineffective this year, posting a 3-8 mark to go along with a 5.23 ERA. He also has a 1.419 WHIP, the worst of his career for a full season.

"We're excited to add a starting pitcher of Ian's pedigree," said Padres general manager Josh Byrnes. "He is under club control through 2015, and we feel he will help us take another step forward as a team."

Thatcher, meanwhile, has appeared in 50 games for the Padres and is 3-1 with a 2.10 ERA. Left-handed hitters have batted just .215 against him.

The 31-year-old will be expected to bolster an Arizona bullpen that has blown 19 saves this season.

Stiles, a 17th-round draft choice of San Diego in the 2011 Draft, went 2-2 with 14 saves and a 2.08 ERA over 46 appearances for Double-A San Antonio before landing on the disabled list last week due to appendicitis.