HOUSTON -- Right-hander Taijuan Walker experienced the nerves that typically accompany major league debuts, but those jitters were fleeting. When it came time for Walker to perform, pitching well came naturally.
Walker, the Seattle Mariners' top prospect, defeated the Houston Astros 7-1 Friday night at Minute Maid Park to record his first career victory.
Walker (1-0) mixed an assortment of secondary pitches that complemented a four-seam fastball that routinely hit 96 mph. Ranked by MLB.com as the fourth-best prospect in baseball, Walker showcased that talent by stifling the Astros (44-90) throughout his five-inning stint, facing just four batters over the minimum and doing so breathlessly.
"My fastball command was all right," Walker said. "Them not ever seeing me before and me not ever seeing them I think that kind of gave me a little bit of an advantage."
The Mariners (61-73) supported Walker with a balanced attack. Excluding second baseman Nick Franklin and catcher Henry Blanco, each member of the lineup reached base via hit or walk. Center fielder Dustin Ackley finished 4-for-5 with four RBIs and also produced a spectacular sliding catch at the wall to cap the bottom of the fifth inning.
Ackley set a career high with those four hits and matched his single-game high for RBIs, set on May 4 against the Toronto Blue Jays. He extended his hitting streak to seven games by stroking hits to four different quadrants of the field, following his single down the right-field line in the fourth inning with a single to right-center in the fifth, a triple to straightaway center in the eighth, and a single to left in the ninth.
"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," Ackley 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."
Walker retired the first eight batters he faced before his defense cost him an unearned run with two outs in the bottom of the third inning.
Mariners left fielder Raul Ibanez failed to make a leaping grab on a line drive that was scored as a double for Astros shortstop Jonathan Villar. Robbie Grossman followed with a routine grounder to shortstop Brad Miller, but Justin Smoak dropped the ensuing throw at first base, allowing Villar to score from second and giving Houston a 1-0 lead.
Walker allowed another hit that ricocheted off the glove of third baseman Kyle Seager. But he was able to limit the damage to one run, and it was that ability to manage that crisis that caught the attention of Seattle manager Eric Wedge.
"It was probably the only time I said something to him over the course of the evening coming off the field," Wedge said. "I really liked the way he handled himself. It didn't speed up on him and he kept his mind in the moment. The focused stayed with him."
Walker resumed a deft mix of upper-90s fastballs, cutters and disarming change-ups. He was lifted after 70 pitches having allowed the one unearned run on two hits and one walk with two strikeouts over five innings. Walker wasn't dominant, but flashes of a plus repertoire were evident.
"He's got electric stuff," Astros right fielder L.J. Hoes said of Walker. "He's got a 98 mile-per-hour (fastball), a 91 mile-per-hour cutter, and he's tough. He kept us off-balance, and he's very tough to hit.
"He was really impressive. He's a big kid (6-foot-4, 210 pounds). On his video, he didn't look as big as he really is. It says he's throwing 96, but it seems way harder than that because he's so big."
Meanwhile, Astros right-hander Brad Peacock (3-5) scuffled, allowing back-to-back RBIs to Ackley and Abraham Almonte in the fourth inning before Ackley chased Peacock with a two-run, two-out single in the fifth.
Peacock departed with the Astros trailing 5-1. He had posted a 2.88 ERA in four starts since his recall from Triple-A Oklahoma City, but on Friday Peacock proved unable to duplicate that magic.
"I felt like I had made great progress until I had this rough one," Peacock said. "But I'll move on from it and be ready for that next one."
NOTES: While Walker made his major league debut 17 days after turning 21, Blanco celebrated his 42nd birthday on Thursday. Walker was one month shy of his fifth birthday when Blanco made his big league debut on July 15, 1997, with the Los Angeles Dodgers. ... Walker and Almonte are the ninth and 10th Mariners to make their major league debuts this season. ... With rookie league Greenville clinching a postseason berth on Thursday night, five Houston minor league clubs are playoff-bound, including all four full-season affiliates.