For Owens, who will wear No. 60, this is his first career major league stint. The 23-year-old is 3-8 with a 3.16 ERA (43 ER/122.1 IP) in 21 starts for the PawSox this season, leading all qualifying Triple-A pitchers with a .193 opponent batting average (84-for-435). He also ranks among International League leaders in strikeouts (3rd, 103), WHIP (3rd, 1.14), and innings pitched (7th). Since June 14, Owens has held teams to two earned runs or fewer in seven of his last nine outings, including each of his last four, registering a 2.64 ERA (17 ER/58.0 IP) and 0.93 WHIP (14 walks, 40 hits) with eight quality starts in that span. Signed by the Red Sox as a supplemental-round selection in the 2011 June Draft (club's third pick, 36th overall), the California native has a 43-24 record and 3.30 ERA (190 ER/518.0 IP) with 572 strikeouts in 96 career minor league appearances (95 starts). Last season, he was named to Baseball America's Minor League All-Star First Team after leading all minor leaguers in wins, going 17-5 with a 2.94 ERA (52 ER/159.0 IP) in 26 starts between Double-A Portland and Pawtucket. Over the last two seasons (2013-14), no other minor league pitcher recorded more strikeouts than Owens (339), the Red Sox' 2013 Minor League Pitcher of the Year.
Cook, 28, was acquired from the Oakland Athletics on Friday in exchange for a player to be named later or cash considerations. He was added to the active major league roster on Sunday, but did not appear in the game. The right-hander has spent the majority of this season with Oakland's Triple-A Nashville affiliate, going 4-1 with eight saves, a 4.05 ERA (15 ER/33.1 IP), and 26 strikeouts in 30 relief outings. In four major league appearances for the A's from April 26-May 2, he went 0-2 while allowing five runs in 4.1 innings. A member of the 2012 American League All-Star Team, Cook is 13-12 with 17 saves, a 2.93 ERA (66 ER/202.2 IP), and 207 strikeouts in 212 career major league outings, all in relief, between the Arizona Diamondbacks (2011) and A's (2012-15). He was originally selected by Arizona in the 27th round of the 2008 June Draft.
With the transaction, the Red Sox 40-man roster is full.