SCOTTSDALE, Ariz. -- It¡¯s that time of year where pitchers tinker with new toys in their arsenal, and Justus Sheffield showcased his latest weapon on Sunday.

Sheffield unveiled a two-seam fastball in the Mariners¡¯ 8-4 loss against the Giants, which helped him to five strikeouts against the 11 batters he faced in what was yet another gem in his superb spring.

¡°Honestly, from pitch one today, beginning in his bullpen, that was the best I ever caught from Justus Sheffield,¡± catcher Tom Murphy said. ¡°He threw his two-seamer exclusively. That was something he wanted to do. He put it on himself. It was the most natural that I¡¯ve seen his fastball move.¡±

Here¡¯s the how and why for Sheffield¡¯s new pitch:

The genesis
The nudge came from Mariners pitching coach Pete Woodworth at the onset of Spring Training. Sheffield lacked effectiveness with his four-seamer, and with incredibly low spin, it became unreliable and predictable -- not ideal for a pitch he threw nearly 50% of the time, and one that opposing hitters were hitting .299 and slugging .507 against, per Statcast.

Two-seamers have taken a back seat in this era of high-spin, high-velocity fastballs that many of the game¡¯s best strikeout artists are utilizing at the top of the zone (Gerrit Cole, Max Scherzer, et al.). But Sheffield doesn¡¯t quite possess their high-90s velocity, meaning a sinking two-seamer with run might be more conducive for his game. Two-seam fastballs typically elicit more grounders and soft contact.

¡°His four-seam had very low spin to begin with, so him switching to a two-seamer actually is going to benefit him in the long run, and you saw that today,¡± Murphy said. ¡°It¡¯s one of those things where you kind of want to feed the beast, right? If a four-seam necessarily isn't at the upper echelon, then why keep pushing something that isn't going to be a great pitch? When you can make it a two-seamer, now all of a sudden, that low spin rate plays to his advantage.¡±

¡°We kind of just saw with the four-seam, he's been working on it a while. It¡¯s what he's always thrown,¡± Woodworth said. ¡°But his other pitches are off his two-seam grip, so they were kind of contrasting ideas.¡±

The installation

During the first inning on Sunday, Sheffield pushed left-hander Mike Yastrzemski into a two-strike count, then punched him out with a nasty slider away. He did the same to Jaylin Davis in the second. Both were set up with his two-seamer, and none of his five strikeouts came from Sheffield¡¯s new pitch. But he¡¯s not necessarily turning to it for wipeout swing-and-miss.

¡°Being able to do that against a righty makes the plate 20 inches wide as opposed to 17. ¡­ Now that right-hander has to respect a larger portion of the inner half, and then that slider can play off even deeper,¡± Murphy said.

By any scouting measure, Sheffield¡¯s slider ranks as elite. He generated 29 of his 37 punchouts last year on it and generated a swing-and-miss 47.5% of the time. His changeup is touted too. But Sheffield needs an effective bridge to those secondary pitches, and fastball command -- and confidence -- remains perhaps the most important aspect of his approach.

¡°I'm going to start throwing the two-seam a lot, just for more movement,¡± Sheffield said. ¡°Give a different look for the hitters. And then my four-seam gets run already, so why not change to a two-seam grip to get some more run? ¡­ It's got me excited, learning a pitch that quick and being able to throw it out there.¡±

The future

In a very small sample size, and with the caveat of Spring Training statistics, Sheffield has a 41.3% strikeout rate over three outings. Since he was acquired as the key return in the James Paxton deal, the Mariners have been bullish on the left-hander¡¯s potential as a key cog in the rotation despite pundits suggesting that he¡¯s destined for a relief role.

The Mariners are hopeful that Sheffield¡¯s ability to make a pretty significant adjustment, and to do so with the in-game conviction he showed on Sunday, are signs of a promising Major League starter.

¡°To me, the highlight today was Sheff really kind of solidifying himself as that guy that we hoped he would be,¡± manager Scott Servais said. ¡°We're seeing it.¡±