OAKLAND, Calif. -- On the mound, Felix Hernandez exhibits all the poise and confidence of a veteran. It's afterward when he shows signs of his true age, giggling and fidgeting with his towel as he discusses his day.
"My age doesn't matter," Hernandez said. "I'm a good pitcher. ... Once I'm on my game, I can't fail."
Yuniesky Betancourt had a triple for Seattle, which handed the A's their fifth loss in six games -- their third shutout defeat in five games and AL-high 12th this year.
The 19-year-old Hernandez (3-2) pitched seven shutout innings to beat A's rookie Joe Blanton, efficiently getting groundout after groundout and giving up just one fly ball that reached the outfield.
"He stuck it to us," A's manager Ken Macha said.
The A's dropped 1½ games behind the Los Angeles Angels in the AL West race and also 1½ games back of the New York Yankees in the wild-card standings. Oakland lost two of three to New York in a weekend series, then dropped the opener of an important series against last-place Seattle that the A's would like to win to keep pace.
The A's quickly understood the hype around Hernandez in the club's first glimpse of the dominant right-hander, who made his seventh major-league start.
Hernandez's first three pitches were fastballs clocked at 96, 98 and 97 mph, then he struck out leadoff hitter Mark Ellis with an 83 mph curveball.
Hernandez hasn't allowed more than three runs in any of his outings, though he lost 2-0 to Randy Johnson and the Yankees in his previous start last Wednesday despite pitching eight strong innings.
Mariners manager Mike Hargrove planned to let Hernandez finish the game before he ran into trouble in the seventh. There were no complaints from the pitcher when he got pulled.
"Felix, if he had a mouth full of nickels he wouldn't give you change for a quarter," Hargrove said. "He doesn't speak much."
Dan Johnson followed with a single -- snapping an 0-for-13 slump -- to put runners on the corners and Hernandez received a mound visit from pitching coach Bryan Price. Scutaro walked to load the bases for Nick Swisher, who flied out to left on a 3-2 pitch to end the threat.
"I lost a little bit of concentration, then decided to center myself, and when I do that, I cannot fail," Hernandez said.
Macha watched tape of Hernandez and said he has "the best stuff of anybody we've faced this year."
Hernandez allowed four hits, struck out five and walked one in a 107-pitch performance. J.J. Putz and George Sherrill tag-teamed the eighth and Eddie Guardado worked the ninth for his 30th save in 32 tries, completing the five-hit shutout.
Guardado became just the fourth Seattle pitcher with 30 or more saves in a season.
He certainly has been impressed with Hernandez.
"He's one of those guys who comes around every 20 years," Guardado said before the latest gem.
Seattle loaded the bases against Blanton in the sixth when Richie Sexson was hit by a pitch, then Beltre broke up a scoreless game with a sacrifice fly to left moments later. Dobbs followed with an RBI single to center.
Blanton (8-11) has lost two straight after a three-game winning streak. The rookie right-hander -- who at 24 seems old compared to Hernandez -- has allowed two or fewer runs in each of his last nine outings.
"I try not to worry about it," Blanton said. "Keeping us in the game is my job. I faced a young guy with great stuff, but there's nothing I can do about it."
Blanton gave up two runs and seven hits, struck out four with two intentional walks in 6 1/3 innings.
"He has pitched tremendously and I've said that to him several times to keep the faith and one of these days we'll get him a bunch of runs," Macha said.
- Hernandez has struck out 50 while walking only 10.
- The Mariners activated RHP Rafael Soriano from the 60-day disabled list. He hasn't played this season after having elbow ligament replacement surgery last year. Hargrove will "use him as we can," but the pitcher won't go more than one inning for now.
- A's CF Mark Kotsay missed his eighth straight game with soreness in his back but is expected to play Tuesday.
- No. 2 Oakland starter Rich Harden, nursing a muscle strain in his right side, made 20 throws on flat ground from 90 feet before the game. The A's hope to have him back on the mound Sunday at Texas, though trainer Larry Davis hinted that timeline could be optimistic. "Everything has to go perfect," Davis said.