The Padres and A's pulled off a one-for-one deal late Tuesday afternoon, sending reliever Luke Gregerson to Oakland in exchange for outfielder Seth Smith.
It adds to an already busy day for the A's, who acquired outfielder Craig Gentry from the Rangers and closer Jim Johnson from the Orioles.
Gregerson has been one of the most reliable setup men in baseball over the last few years, posting a 2.71 ERA over 66 1/3 innings in 2013 with San Diego. The 29-year-old is 17-22 with 16 saves, a 2.88 ERA and 352 strikeouts against 107 walks in 363 relief appearances over his five-year big league career (all with the Friars, 2009-13).
Smith, 31, hit .253 with 27 doubles, eight home runs and 40 RBIs in 117 games for Oakland last season. He started 97 of those games -- 46 as the designated hitter, 43 in left field and eight in right field. Smith returns to the National League West after being selected by the Rockies in the second round of the 2004 First-Year Player Draft and breaking into the big leagues with Colorado.