Pineda, a 6-foot-5, 22-year-old Dominican native, struck out one in his first outing since pitching in an intrasquad game last week. He threw 14 of his 22 pitches for strikes and did not walk a batter.
The 255-pound right-hander, who went 11-4 with a 3.36 ERA and 154 strikeouts between Double-A West Tenn and Triple-A Tacoma in 2010, is on a quest to make the Mariners' rotation this spring. He features an upper-90s fastball and a solid slider-change combo that helped him go 8-1 with a 2.22 ERA in 13 starts in the Southern League last summer.
"His demeanor out on the mound and understanding of what he wants to do is impressive for a young guy," Mariners catcher Adam Moore, who caught Pineda last year at Tacoma, told MLB.com on Tuesday.
"When you ask him what he's thinking, he has an idea of what he's doing with location and pitch selection. He's growing. And with that big body out there and his deception, he's going to be something special."
Pineda signed with Seattle as a free agent in 2005 and has navigated the farm system ever since, earning a spot at No. 13 on MLB.com's Top 50 Prospects list for 2011.
He's widely considered the organization's top pitching prospect and perhaps the club's top young talent outside of former first-round pick Dustin Ackley.
"He's an intimidating presence," Mariners infielder Brendan Ryan said to MLB.com. "Throwing the ball that hard with some movement, it's a wonderful thing."