SEATTLE -- This is the Justus Sheffield the Mariners have been waiting to see.

Sheffield, the promising left-handed prospect acquired from the Yankees in the James Paxton trade prior to the 2019 season, picked up his first Major League victory on Sunday with six scoreless innings in Seattle¡¯s 5-3 win over the Rockies.

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The 24-year-old Tennessee native allowed just four hits with no walks and seven strikeouts while equaling the longest outing among his 10 MLB starts. Sheffield had gone 0-2 with a 9.39 ERA in his first two starts this year and was 0-3 with a 6.18 ERA in 10 career outings with Seattle, including nine starts, since being called up last Aug. 23.

Sheffield has shown flashes of his considerable promise at times, but he finally pieced together a complete outing against a tough Rockies club that had won seven of its past eight and leads the National League West at 11-4.

¡°It means everything,¡± Sheffield said of securing his first win. ¡°It means the world, honestly. Not only for myself, but to come out and finish this series with a win before we get on the flight is always great. I¡¯m definitely happy and excited about that.¡±

For Sheffield, only one thing was missing. Players traditionally are subjected to a postgame celebratory ¡°beer shower¡± after attaining a career first, with teammates dumping anything available on their heads as they get washed down. But these aren¡¯t typical times with physical distancing in the clubhouse, so Sheffield emerged unscathed there as well.

¡°I actually lucked out,¡± Sheffield said with a smile.

For the Mariners, however, there was plenty to celebrate, as they watched one of their prize young pitching prospects start to pay off. Sheffield and Justin Dunn -- who¡¯ll start Monday¡¯s series opener in Texas -- are two rookies in the rotation who figure as big parts of the rebuilding plans.

¡°It was an awesome performance by Sheff,¡± Mariners manager Scott Servais said. ¡°Really fun to watch. He¡¯s a young guy and we¡¯ve seen some outings like that leading into this in Spring Training and Summer Camp. But to see him perform on the main stage here was awesome to see. He was in total command all six innings he was out there. The future is very bright for him.¡±

Sheffield worked ahead in the count all day, mixing a low-90s fastball with a nasty slider, with six of his seven strikeouts coming on the slider.

¡°It¡¯s a wipe-out pitch, a pitch that as he continues to get comfortable with, he¡¯s able to land it for strikes, take it down and into the righties,¡± Servais said. ¡°His pitch usage and what he¡¯s doing is a little different. He¡¯s really gone primarily to the two-seam fastball, living in the bottom of the strike zone. In today¡¯s game, a lot of people want to ride the ball up at the top of the zone. But it¡¯s got to be your strength. We¡¯ve found Sheff¡¯s strength is at the bottom of the zone, working the two-seamer and the slider and then some really good changeups in there today as well.¡±

That strategy worked wonders against a Rockies team with one of the Majors' most productive offenses.

¡°On his breaking ball, we just couldn't get a handle on it,¡± Rockies manager Bud Black said. ¡°We don't have a lot of history with him. We looked at a lot of video. We talked about his stuff. It was a little bit different than what he did last year and a little bit different approach. It looked like he was trying to have a running fastball, as opposed to a four-seam fastball with more velocity.

¡°I've seen him up to 95-96 mph with the fastball. Today was like 90-91 with some two-seam run. You saw that against the left-handed hitters, a little bit of tail and run to his fastball. The breaking ball was effective today, there's no doubt about it. Out of the hand, it looked like a strike, maybe mid-thigh, and then in the hitting area, it had good action. It was down underneath our right-handers' swings and sort of moving away from our lefties."

Combine that with Sheffield¡¯s bulldog mentality and the youngster brings a lot that the Mariners can build on.

¡°I loved his presence on the mound,¡± Servais said. ¡°He had a little swag to him and confidence. He wanted to be out there. He wanted the ball. 'Here it is, hit it' -- that¡¯s the mentality all our guys need to take.¡±

Sheffield¡¯s efforts helped Seattle snap a three-game losing streak, as Dylan Moore provided the early lead with a two-run homer in the first off Germ¨¢n M¨¢rquez. The Mariners took advantage of a pair of errors on the same play by Colorado third baseman Chris Owings to push across three unearned runs in the seventh and then withstood a late Rockies rally as they closed out a 3-7 homestand and now are 6-11 heading to Texas to start an eight-game trip.