O'Neill, the Mariners' No. 2 prospect, according to MLBPipeline.com, is one of just three non-pitchers or catchers among the players invited in addition to those on the 40-man roster.
"He had arguably the most impressive season of any of our Minor League guys last year, when you consider the context," assistant general manager Jeff Kingston said. "He was 20 years old in Double-A. Going from [Class A Advanced] to Double-A is the toughest jump to make in the Minors, and this kid made it as one of the youngest players in the league."
Outfielder Kyle Waldrop, who played 15 games for the Reds last year, is one of the veteran non-roster additions. Shortstop Tyler Smith, ranked 30th, is also coming to camp for a second straight year.
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Moore, the club's No. 8 prospect, is among the 10 non-roster pitchers invited, and will be given a good look.
"Andrew isn't necessarily going to wow you with his stuff, not like the second coming of Felix [Hernandez] when he was 19 years old and throwing 96 mph, but he has that 'it' factor," Kingston said. "Just the makeup, character, preparation -- he knows how to pitch. He has a unique ability to slow the game down, make pitches and get hitters out. We're not sure if he'll start the year in Double-A or Triple-A, but there's a pretty good chance you'll see him at some point this year [in the Majors]."
Other right-handers are Christian Bergman, Cody Martin, Micah Owings, Max Povse, Peter Tago, Dylan Unsworth and Ryan Weber. Lefty Dean Kiekhefer also drew an invite, as did switch-pitcher Pat Venditte.
Non-roster catchers coming to camp will be Nevin Ashley, Steve Baron, Marcus Littlewood, Tyler Marlette and Sebastian Valle.
Povse, a 6-foot-8 right-hander, is the club's No. 9 prospect after being acquired in a trade from the Braves. Marlette is ranked 28th.