Walker has now thrown eight shutout innings with just two hits, one walk and eight strikeouts. He didn't allow a hit Saturday and worked impressively out of a second-inning jam after a two-base error on third baseman Kyle Seager, his lone walk of the game and a passed ball put runners on second and third with just one out.
Walker emerged unscathed from that situation with some strong pitching and escaped injury the following frame when a nasty line drive by D-backs shortstop Cliff Pennington deflected off his glove and caught him flush in the stomach. Walker picked up the ball and fired to first to get the third out, but was removed an inning before his expected finish after trainers checked him out.
"I'm fine," Walker said. "But it came in pretty hot."
Walker was good enough to be sent to the bullpen to throw another 21 pitches and build his final pitch count to 65 as closer Fernando Rodney came in to take the fourth inning against the D-backs.
Walker showed something in the second when he got a force out at home for the second out with runners on second and third, then dug deep to strike out Danny Dorn after falling behind 3-0.
"When I was younger I'd get men on base and I'd get frustrated and try to do so much so they wouldn't score and it kind of got me in trouble," Walker said. "This year I'm keeping my composure when people get on and just work for ground balls and get the easy outs."
"He showed a lot of poise when we made a mistake there and put him behind the eight-ball," said manager Lloyd McClendon. "He kept pitching, pounded the zone and did a nice job. I think he's come a long way from September of last year. He's grown quite a bit."
It's that maturation process the Mariners are eager to see as their talented right-hander competes for a starting spot. Veterans Felix Hernandez, Hisashi Iwakuma and J.A. Happ are locks, while young southpaw James Paxton figures to have a spot as well if he can get healthy.
Paxton missed the first few weeks of camp with a bruised forearm, but is slated to throw his first game action Tuesday in a three-inning simulated situation and should have time to be ready for the start of the season barring any setbacks.
That leaves Walker competing with Roenis Elias, who won 10 games last year as a rookie, as well as outside candidate Erasmo Ramirez for the fifth spot in the rotation.
At this point, it's a far different situation than 2014 when Iwakuma, Walker and Brandon Maurer were hurt all spring and veterans Randy Wolf and Scott Baker didn't work out. So the Mariners depth -- further bolstered by the recent signing of veteran right-hander Kevin Correia to a Minor League deal -- is in far better shape.
"You look at last year, we didn't have that," McClendon said. "We were a mess leaving Spring Training. It's nice to have that depth and knock on wood it will stay that way."