• Mariners acquire 3 lefty prospects for Lowe
"He's got a good, hard sinker and is a real solid makeup kid with good intangibles," Mariners general manager Jack Zduriencik said.
Sampson, who will report to Triple-A Tacoma, went 8-8 with a 3.98 ERA in 21 starts for Triple-A Indianapolis, leading the International League in starts and ranking third in innings pitched (124 1/3) and fourth in strikeouts (95).
Happ was 4-6 with a 4.64 ERA in 21 games (20 starts) with the Mariners after he was acquired last winter from Toronto for outfielder Michael Saunders. Happ will be a free agent at the end of the season.
"He hadn't pitched well his last two-to-three outings and it was tough," said manager Lloyd McClendon. "But nobody feels worse than him. He's a competitor and he wanted to win and do well for this team, and it just didn't work out."
Happ's spot in the rotation will need to be filled before his next scheduled outing Tuesday in Colorado, which Zduriencik said would come from within the organization. Roenis Elias, who was 4-6 with a 4.27 ERA in 13 starts for Seattle earlier this season, is a logical candidate to be recalled from Tacoma to fill that slot.
For now, the club is adding two newly acquired relievers to the bullpen to take the place of Happ and Mark Lowe, who was also traded Friday to the Blue Jays.
Left-hander Rob Rasmussen, who was one of three pitchers acquired for Lowe, will join the team along with right-hander Jose Ramirez, who came from the Yankees on Thursday in a trade for Dustin Ackley. Both are expected to be available for Friday's game against the Twins.
The Mariners added six young pitchers and one outfielder in their three Deadline deals in exchange for Ackley, Lowe and Happ.
Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB, read his Mariners Musings blog, and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.