Sheffield (1-2), one of three pitchers 24 or younger in the Mariners' starting rotation, gave up four hits without a walk and struck out seven in his longest stint of the season. He worked his way out of a jam with a strikeout to end the fifth, then sat down two more Rockies in the sixth before reaching his pitch limit.
''That was my main thing: Get to two strikes as quick as possible and put them away,'' Sheffield said. ''I really didn't want to mess around.''
Sheffield never reached a 2-0 count and landed 16 first-pitch strikes against the 22 batters he faced. The lefty was especially effective with his slider.
''It's really good,'' Seattle manager Scott Servais said. ''It's a wipeout pitch.''
Charlie Blackmon extended his hitting streak to 13 games with a first-inning double for Colorado. He also got help from a strange bounce past second baseman Dee Gordon for a single in the fourth.
The loss snapped a three-game win streak for the Rockies, who had won seven of eight in August - including two straight over the Mariners. The defeat also ended a six-game interleague win streak.
Colorado starter German Marquez (2-2) struck out four and walked one in seven innings. He gave up six hits, including Moore's third home run.
Fielding and throwing errors by third baseman Chris Owings on Kyle Seager's routine grounder helped end Marquez's outing as the Mariners added three unearned runs in the seventh to avoid a series sweep. Evan White, Tim Lopes and Gordon each drove in a run.
''If you win series, you're going to have a good season,'' Rockies manager Bud Black said. ''We've done that so far. If we play good baseball and we let our talent show, we're going to win games. If we continue to pitch the way we have been, our bats will come around.''
Rockies: Black gave slumping 3B Nolan Arenado the day off to rest.
Mariners: Hot-hitting C Austin Nola was an unexpected scratch from the lineup while continuing to deal with a swollen wrist. Servais said Nola was having trouble swinging the bat without pain after injuring his wrist Friday.
Rockies: RHP Jon Gray (0-1, 3.31 ERA) takes the mound Monday at home against Arizona.
Mariners: RHP Justin Dunn (0-1, 6.43) makes his third start at Texas.
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