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.”