PEORIA, Ariz. -- Scott Servais knew that the Padres’ fearsome foursome awaited in the third inning of the Mariners' Cactus League opener Friday afternoon, which is precisely why Seattle's skipper installed Prelander Berroa, the under-the-radar prospect who might quickly become mainstream.

Berroa struck out Xander Bogaerts and Nelson Cruz as part of a three-K third then returned for a 1-2-3 fourth, raising eyebrows from Seattle’s dugout, which has quickly caught on to his potential the past two weeks, and San Diego’s, a World Series favorite.

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“I was a little nervous going up there because obviously these are guys that I grew up watching,” Berroa said through an interpreter. “But I kind of told myself that I do have to kind of keep my composure and go out there and do my job.”

The 22-year-old is the Mariners’ No. 15 prospect, per MLB Pipeline, but will jump when the 2023 rankings are revealed next week. A case could be made that the Dominican Republic native might have the best raw stuff in the pipeline, with a top-end fastball and slider combo that was on full display Friday. Berroa sat in the mid-90s and hit 99 mph with the heater, according to scouts, while landing the breaking ball for strikes.

The velocity jumps out, but it’s the slider that will soar him to the big leagues -- at this rate, almost certainly this season. 

“The spin would tell you that it's going to have more lateral movement than it does,” catcher Tom Murphy said. “And so that type of spin -- and it just going straight down -- it's kind of a deceptive pitch for hitters to get used to. And even on his arm side, it seems to come back almost like screwball-type effect on his arm side. And then when it's over the plate, it's like straight down.”

Berroa, who profiles for leverage relief long term, used the slider for each of his strikeouts of Bogaerts and Cruz. The pitch really took off in 2021, Berroa says, when he adjusted the grip.

“It's been very successful for me because I feel like it's one of the pitches that I can control the most from any of my repertoire,” Berroa said. “It's one that I can hit the strike zone on when I want to.”

Said Murphy: “It's a really funky pitch. The delivery out of the arm slot is kind of straight over the top, so I think he's going to be really effective for us, just based off that pitch alone.”

It’s super early and only one Cactus outing in his first big league camp, but Berroa -- whom the Mariners acquired from the Giants for infielder Donovan Walton last May -- already looks like a steal.

Beyond his pure stuff, the sneaky athleticism and acumen is what’s stood out most to Mariners brass since he joined the organization. He also has absorbed what they preach in terms of pitch usage and location and count management. 

“Ignorance is bliss sometimes,” Servais said. “You just get out there, you throw hard, hopefully you throw strikes -- and he has a history of throwing strikes, certainly with the breaking ball. He's got to work with the fastball, but a lot to like there and a lot of upside for him.”

Berroa originally signed with the Twins as an infielder for $200,000 in 2016, making this his third organization. This spring, he’s absorbing insights from fellow Dominican Republic native Luis Castillo and the rest of Seattle’s loaded pitching staff.