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8/31/2013 7:57 P.M. ET

Walker becomes youngest Mariner to win debut

HOUSTON -- When Taijuan Walker shut down the Astros for five innings on two hits and one unearned run on Friday, he became the youngest Mariners starting pitcher ever to win his Major League debut.

Walker, at 21 years and 17 days, replaced Travis Blackley, who beat the Rangers in 2004 at the age of 21 years, 240 days. The club's top pitching prospect became just the 11th pitcher in Mariners history to win his starting debut and just the second -- joining Pat Rice in 1992 -- to not allow an earned run in the process.

Erik Hanson is the only other Mariners starter besides Walker and Rice to not allow an earned run in his debut, but he lost his opener in a 2-0 decision to the Twins in 1988.

Walker gave up just a tough-luck double off the glove of left fielder Raul Ibanez and a single that third baseman Kyle Seager couldn't backhand, though he did benefit from excellent defensive plays by second baseman Nick Franklin and center fielder Dustin Ackley.

"He had pretty good stuff," said veteran catcher Henry Blanco, who at 42 was twice as old as his teammate on the mound. "He had all four pitches going good and mixed it up real well. He kept hitters off balance and that's what you've got to do here in the big leagues. He worked ahead of hitters. That was pretty impressive."

Equally impressive was Walker's poise and presence.

"He acted like he'd been here before," said Blanco. "I thought he was going to be nervous the first couple hitters, but he wasn't. He got ahead of hitters and went from there."

Even when his defense let him down with two misplays in the third inning that led to the unearned run, Walker kept focused.

"I don't think it bothered him at all," Blanco said. "You could see right after that, he just kept going after hitters. He deserved the win."

Walker's next start will be Wednesday at Kansas City.

Ackley gaining confidence in center and at plate

HOUSTON -- A year of transition for Dustin Ackley is turning into a breakout second half as the Mariners new center fielder has begun putting things together both at the plate and in the field.

As the second pick in the 2009 First-Year Player Draft, Ackley carried high expectations upon arrival in Seattle two seasons ago. But after struggling through 2012 and the first half of this year, the 25-year-old finally seems to have found his comfort zone.

After going 4-for-5 with a triple and four RBIs in Friday's 7-1 win over the Astros, Ackley was batting .411 (30-for-73) in August and .364 (40-for-110) since the All-Star break, raising his season average from .205 to .261. And in the outfield, he unleashed his best moment since transitioning from second base in midseason when he made an outstanding catch of a ball deep in the right-center gap to rob Robbie Grossman of an extra-base hit.

Manager Eric Wedge noted Ackley has played somewhat cautiously in the outfield as he's felt his way through the new position, but was able to let loose on Friday's aggressive catch in the fifth on a ball he hauled in at the base of the hill in Minute Maid Park's unique configuration.

"It's been somewhat unfair to him having to learn on the fly up here in center field," Wedge said. "I know he had a little bit of time in Triple-A, but that's tough to do up here with the speed of the game and different ballparks.

"There've been a few balls where if he kept going as fast as he is, he might have gotten to that he pulled up on, which is normal just because you don't know the ballpark and you're trying to be smart and make the right play. But that was one there where he kept going and made a heck of a catch. You see his progress whether it be jumps on the ball or routes or angles. You really see him getting better from week to week."

"Everything for me in the outfield is kind of learning on the fly," Ackley acknowledged. "Just how to approach balls. I've never had a play where I've slid like that at the wall and had to avoid running into it. Everything for me right now is just learning different plays and different things, especially with the hill out there."

Ackley has less to learn about hitting, which is something he's always done at every level until he batted just .226 last year and then struggled at the .200 mark until a midseason demotion to Triple-A Tacoma. But after toying with a new stance, he's finally gotten back to feeling comfortable at the plate again as well.

He got hits to left, center and right field on Friday, a welcome sign that he's seeing the ball well and hitting where he's pitched now.

"And different types of pitches, too," Wedge said. "He turned around that fastball late with the bases loaded right back up the middle. The breaking ball to right field, the changeup to left field. You know what? You can really see his confidence growing, you can see his feel for the game getting better, his feel for different situations getting better, too."

For Ackley, it's just getting back to being what he's always been, a natural hitter.

"Yeah, I think now it's just something where I can really trust in my swing, where before I didn't really trust it and all that," he said. "Now it's gotten back to how it used to feel and that's why I'm mentally focused every at-bat and ready to hit."

Mariners plan to call up reliever Wilhelmsen

HOUSTON -- Major League clubs can expand their rosters on Sunday when the September callups are allowed beyond the normal 25-man rosters, and former closer Tom Wilhelmsen will be one of the players the Mariners bring up in the next few days.

Manager Eric Wedge declined to say what other players will be added, but acknowledged Saturday that Wilhelmsen will rejoin the club despite a rough time with Triple-A Tacoma since his demotion a month ago.

Wilhelmsen is 0-1 with a 10.50 ERA in 12 innings over eight games, allowing 19 hits and 14 runs with 15 strikeouts and five walks. He allowed four hits and four runs while getting only two outs in his last outing before being replaced after throwing 30 pitches.

"I want to get him back up here and see where he's at," Wedge said. "It's not always indicative of what you're seeing down there. A couple years ago was a great example with him. Once he gets back up here and gets comfortable again and we have a good chat with him and break him back in up here, he's not too far removed from having great success up here. We can't forget about that."

Wedge indicated a few players would be called up Sunday, while several others would wait until after Tacoma's season ends on Monday, presumably joining the team Tuesday in Kansas City.

Another player certain to be added is catcher Mike Zunino, who continued his injury rehab assignment Friday by going 1-for-4 with a run scored as the designated hitter in Tacoma's 7-1 win over Sacramento. Zunino, recovering from a broken hamate bone in his left hand, has hit .143 (2-for-14) with four runs, a triple and three walks in four games.

Pitcher Erasmo Ramirez will also rejoin the club in time to make his next scheduled start on Tuesday after being reassigned to Tacoma on Friday in order to make room on the roster for outfielder Abraham Almonte.

Worth noting

Kyle Seager was in the starting lineup Saturday for his 88th consecutive game, the longest stretch of starts by a third baseman in club history. Adrian Beltre held the previous best of 86 from 2005-06.

Seager's streak is the seventh longest in the Majors by a third baseman over the past five years and second-longest active streak, trailing only the 184 by Baltimore's Manny Machado.

• When Brad Miller and Seager swiped bags in Friday's win, it was the Mariners first two-stolen base game since June 29. Seattle is 28th out of 30 MLB teams in stolen bases with 40 in their first 133 games, ahead of only the Cardinals (38) and Tigers (31).

The franchise record for fewest stolen bases in a full season is 81 in 1989 and 2007. The Mariners stole just 48 bases in 1994, but only 112 games were played in that strike-shortened season.

Greg Johns is a reporter for MLB.com. Follow him on Twitter @GregJohnsMLB as well as his Mariners Musings blog. This story was not subject to the approval of Major League Baseball or its clubs.