TORONTO -- The next wave of top-end talent in the Mariners’ pitching-heavy pipeline has arrived to the Majors, as the club announced Tuesday it has selected the contract of right-hander Bryce Miller from Double-A Arkansas.

Miller, ranked as Seattle’s No. 2 prospect and MLB Pipeline’s No. 88 overall, will start Tuesday’s series opener against the A's in Oakland, and he will remain in the Mariners' rotation for the foreseeable future. The Mariners also announced that infielder Tommy La Stella has been designated for assignment.

After a strong spring but a mostly uneven start to the regular season, Miller could represent Seattle's 2023 replacement for Robbie Ray, who suffered a left forearm strain in his first start. Ray learned last week that the injury would require season-ending surgery.

The Mariners had used Chris Flexen in that spot, but he struggled to a 10.58 ERA in four starts, leading to a transition back to the bullpen, while Easton McGee, who made his first MLB start on Saturday in Toronto, hit the 15-day IL on Sunday with a left forearm strain.

Despite McGee wowing by carrying a no-hitter into the seventh, he was considered more of a spot replacement while the club pondered a more longterm plan.

Enter Miller, who was always destined to contribute in 2023 -- but when would be based on circumstance.

Miller hasn’t wowed since a strong Spring Training, but scouts suggested his stuff has still played up and the mainstream numbers might be more indicative of working on specific developmental points in certain sequences, such as pitches in specific counts.

Opposing hitters have a slash line of .281/.306/.573 (.879 OPS) against Miller with five homers in four starts, over which he’s carried a 6.79 ERA. His strikeout numbers are down, too, with 18 in 19 2/3 innings.

Among the next wave of young Mariners pitchers, Miller was the clear choice over Emerson Hancock, whose development has been slower due to early-career injuries, and Bryan Woo, who has just 74 pro innings, also due to injuries.

Seattle also will re-slot its rotation and push its other starters back to allow Miller to debut against last-place Oakland rather than the 2022 World Series champion Astros on Friday, when the spot was due up next. 

A fourth-round pick out of Texas A&M in 2021, Miller took the biggest leap in the organization in ‘22, climbing three Minor League affiliates while jumping from No. 24 to No. 2 in the Mariners’ prospect rankings. 

Miller was also a strikeout machine, with 163 in 133 2/3 innings for a 30% rate. Most telling, his stuff held up through the rigors of 27 starts, and he missed no time, a byproduct of rigorous arm-care routine, he said. It created the chance for him to make an impression in big league Spring Training this year, and he did just that in four Cactus League outings. 

“I figured my stuff is good enough to throw to the big league hitters -- just go out and prove it,” Miller said in March.

It’s the fortification of Miller's secondary pitches, a curveball and slider, that has him getting the promotion.

“He's got them all, with a changeup on top,” manager Scott Servais said in spring. “It's really, really good. I definitely think it's a starting pitcher mix based on his delivery, his stuff, his demeanor, his whole [profile].

"I think he's a starting pitcher. It doesn't mean he couldn't pitch out of the bullpen, but I see him as a starter.”

To clear a 40-man roster spot for Miller, the Mariners outrighted reliever Diego Castillo to Triple-A Tacoma after passing him through waivers. Castillo could have rejected the outright and become a free agent due to his more than three years of MLB service time, but doing so would have forfeited the remainder of his $2.95 million salary for 2023.

Acquired at the 2021 Trade Deadline, Castillo has experienced a significant decline this year, with a 6.23 ERA in 8 2/3 innings -- during which he’s walked as many hitters as he’s struck out (seven) while also surrendering two homers.

Castillo has also experienced a 1.6 mph decline in average fastball velocity, to 94.2 mph. In an ideal situation, he works through his kinks at Tacoma and contributes later this year.