SEATTLE -- George Kirby didn’t necessarily need another weapon to attack hitters. But after seeing the immediate, in-game returns when Robbie Ray added a two-seam fastball last month, the rookie righty wanted in.

So, in a bullpen session three weeks ago, with Ray and the rest of the rotation observing, Kirby moved his thumb higher to grip inside the seams, fired away, saw the effectiveness of the side spin away from his right-handed release point and had an “aha!” moment when he realized that it could play at the big league level.

“The one he threw last night was nasty,” Ray said after Kirby’s start in Tuesday’s 5-4 win over the Rangers, referencing a called strike three to Nathaniel Lowe that ended the top of the fourth inning.

Against Texas, Kirby needed just 51 pitches to get through five scoreless innings on a night when he was on a 65-pitch and/or four-inning threshold. Part of that incredible efficiency was related to his new pitch (also classified as a sinker), which he threw just six other times but twice used to induce outs on contact. The rookie said that the pitch is more conducive to weak contact, but that it also plays better off his swing-and-miss stuff.

“It’s just a different look for the hitters,” Kirby said. “Being able to get some easier outs, ground balls or something, and really establishing that inside part of the plate. And trying to work the slider off that, too. I thought that’d be a good combo to have. If I’m running out on a righty and then tunneling a slider off that, [the two-seam] might be a good pitch there. ... It kind of prevents [righties] from getting comfortable in the box, if can push them back a little bit with that two-seam and just run it on their hands."

When Ray added the pitch, it was because the Astros were all over him and he needed an answer. Kirby’s situation is far different -- and not just because Ray is a lefty and Kirby a righty. Ray was primarily a two-pitch pitcher (slider and four-seam) before the addition, yet the two-seamer is the fifth pitch in Kirby's repertoire. He has a far denser arsenal, and his other pitches have been highly effective, especially in his surge through Seattle’s Minor League system.

“I’ve always wanted to throw a two-seam, and then I saw how effective it was for Robbie and I was like, ‘Yeah, I want to get it going,’” Kirby said. “It’s just a good weapon using it off the four-seam, too. I’m super four-seam heavy, so getting that little run at the end, it just works.”

The two-seam additions for Kirby, and even more so, Ray, have stood out most. But behind the scenes, there is even more tinkering at play within the Mariners’ rotation.

“It helps when you’ve got guys on the team that throw pitches that you don't,” Ray said. “And so you can just mess around. Like, Marco [Gonzales] throws a changeup, the cutter. I don’t throw either of those, but learning to kind of manipulate a slider to where it can be a little more cutter-ish, or whether it's working on my changeup in catch play. I think it's just a really cool, fun dynamic, where we just kind of pick each other's pitches apart.”

Kirby didn’t get to throw the two-seamer deeper into Tuesday’s outing due to his workload limits, which will continue to be closely monitored in the second half. Mariners manager Scott Servais indicated that the rookie will likely be on another limit on Sunday in Houston, and it’s possible that the team will send him to Triple-A Tacoma again to manage his innings.

He’s already at 96 innings this year between the big leagues and the Minors, way past the 67 2/3 he threw last year. The Mariners intend to have him pitch deep into the season -- and the two-seamer will likely be a big part of his arsenal when he does.