The San Diego Union-Tribune initially reported the deal, multiple outlets confirmed Pomaranz and late Thursday night, the Red Sox announced the deal..
Pomeranz was 8-7 with a 2.47 ERA in 17 starts for the Padres, who obtained him from the Oakland Athletics in the offseason for Yonder Alonso and Marc Rzepczynski. He was not initially in San Diego's rotation when spring training started but became the ace for the fourth-place Padres.
In 102 innings this season, Pomeranz has a strikeout rate of 10.1 per nine innings and a 47.8 ground ball rate. He was named to the National League All-Star team as an injury replacement for New York Mets right-hander Noah Syndergaard.
This is the second time that Pomeranz has been coveted near the non-waiver trade deadline. Five years ago, he was one of three prospects the Cleveland Indians sent to the Colorado Rockies for Ubaldo Jimenez.
Pomeranz struggled with the Rockies, going 4-14 with a 5.20 ERA in 34 appearances (30 starts). The Rockies traded him to Oakland after the 2013 season and he thrived as a reliever. With Oakland, he was 10-10 with a 3.08 ERA in 73 appearances (19 starts).
To obtain Pomeranz, Boston sent right-handed pitching prospect Anderson Espinoza, who received a $1.8 million signing bonus out of Venezuela in 2014. Espinoza has a 5-8 record and a 4.38 ERA in 17 starts with Class A Greenville of the South Atlantic League.
This is the third major trade the Padres have made this season. San Diego has already dealt right-handed starter James Shields to the Chicago White Sox and closer Fernando Rodney to the Miami Marlins.
Thursday also marked the second major trade between the teams in the last year. During the offseason, the Red Sox obtained closer Craig Kimbrel for four minor leaguers.