The 21-year-old Pineda went 11-4 with a 3.36 ERA in 25 starts for Double-A West Tennessee (8-1 with a 2.22 ERA) and Triple-A Tacoma (3-3 with a 4.76 ERA).
"Michael had a breakthrough season and showed his true talent this season," said Pedro Grifol, the Mariners' director of player development. "He was a true competitor at both levels and put his name on the map as one of the most talented pitchers in the Minors."
Pineda, expected to be a late-season callup from Tacoma, has been shut down for the remainder of the season to prevent him from throwing too many pitches.
But he could be one of the favorites to be in Seattle's rotation next season.
He was named the Pacific Coast League's Pitcher of the Week for June 28-July 4 after going 1-0 with 21 strikeouts in back-to-back starts.
It could be a few more years before Poythress becomes a fixture in the Mariners' lineup, but he certainly opened some eyes during his stellar season with Class A High Desert.
He led all Minor Leaguers with 130 RBIs (averaging 1.06 per game), batted .315, hit 33 doubles and 31 home runs in 123 games. He ranked first in RBIs, second in slugging percentage (.580), third in home runs and tied for ninth in batting average.
Poythress was the Mariners' second-round selection in the 2009 First-Year Player Draft out of the University of Georgia.
"Rich had a remarkable season," Grifol said. "He was consistent throughout the season on the road and at home. He put together an impressive season and we are very excited about his future in our organization."
The Mariners also named Jose Castro as the Player Development Staff Member of the Year.
Castro started the season as the Minor League hitting instructor and ended it as the Tacoma manager, taking over for Daren Brown, who replaced Don Wakamatsu as the Mariners' skipper on Aug. 9.