The 22-year-old with ace potential will start the team's Cactus League opener Wednesday against San Diego at the Peoria Sports Complex.
''I feel comfortable, confident, too,'' said Walker, who's vying for the Mariners' fifth starter spot. ''I'm just going to go out there and pretty much give all I have.''
Starting the first game of spring training is a big change from where Walker found himself a year ago when a shoulder injury sidelined him during the preseason.
''I wasn't able to do anything,'' he said. ''I wasn't even able to play catch. To be able to start a game and actually have a spring training is good.''
Walker is competing with Roenis Elias and long-shot Erasmo Ramirez for the fifth starter spot. The Mariners are planning to take an early look at all three. Weather permitting - rain is forecast this week in Phoenix - Elias will start Thursday against the Padres and Ramirez is scheduled to start Friday against the Los Angeles Dodgers. Elias proved last season to be reliable, starting 29 games and posting a 10-12 record, while Ramirez struggled, starting 14 games for Seattle and 14 at Triple-A Tacoma.
Walker knows one spring start won't land him a spot on the big-league roster, but he's also aware that he's in a competition.
''I'm just going to go out there and do the best I can,'' he said. ''So if that means I have to go full speed, then I will.''
Walker is eager to put a new pitch into action. He's been working on adding a slider and the results so far have been positive.
''When I threw it in live BP, the first couple I threw were kind of shaky,'' he said. ''After that it felt really good.''
''I'll throw it quite a bit just to see how it is against hitters.''
Barring injury, the first four slots in Seattle's starting rotation will go to Felix Hernandez, Hisashi Iwakuma, James Paxton and J.A. Happ. The Mariners are expected to have one of the top rotations in baseball and McClendon is excited about its potential.
''I told my guys this, `We all know Felix is one of the best in the game, but there's no law that says you can be just as good as him on this team,''' he said. ''I think our guys are ready for that challenge and we've got some quality arms. We'll see what happens.''
Weather permitting, Iwakuma and Jordan Pries will start split-squad games Saturday, with Iwakuma facing Arizona and Pries against the Chicago White Sox. Happ will start Sunday against Cincinnati.
NOTES: McClendon said CF and leadoff hitter Austin Jackson will be ''the key to our offense'' and he doesn't plan to ask him to do too much. ''If Austin Jackson hits .270 to .275 with an on-base percentage of .340, we'll be OK,'' he said. ''I don't need him to be that guy that hits 25 home runs in the leadoff spot. I just need him to get on base.'' McClendon also wants to see Jackson, 28, play fewer than the 154 games he started last season. ''That's too many for a center fielder with his frame,'' he said. . McClendon said Jesus Sucre has the inside track on landing the backup catcher role behind starter Mike Zunino. He lauded the 26-year-old's ability to handle a pitching staff, play defense and contain runners. Sucre, who played 21 games for Seattle last season, will receive his biggest competition from veteran John Baker, who signed with the team in the offseason. . Erasmo Ramirez and Jordan Pries are slated to start an intra-squad game on Monday, but weather forecasts predict rain and could cancel the game.