"He's got a lot on the ball," said Hargrove. "He's the best young pitcher I've ever seen. I didn't see Dwight Gooden when he was young, but of all the young kids I've seen, he's by far the furthest along."
Hargrove is impressed by the fact Hernandez can go after hitters with a variety of weapons.
"He has a fastball, a curveball, a slider and a changeup," Hargrove said. "He has above average command of all his pitches."
Hargrove is even more impressed by another quality of Hernandez.
"He's very mature for his age," Hargrove said.
Hernandez threw 100 pitches against the A's. Considering his age and the fact he's in his fourth season of pro ball, the Mariners plan on being as cautious with him as possible.
"We're going to try to keep him under 200 innings, but if we're in this thing in the middle of September, we'll probably revisit this," Hargrove said.
Hernandez allowed 61 hits and struck out 77 in 84 1/3 innings last season.
To make room for outfielder Matt Lawton, who was activated after serving a 10-game suspension for a violation of Major League Baseball's drug policy, on the roster, the Mariners designated catcher Guillermo Quiroz for assignment. Quiroz appeared in two of the Mariners' first eight games and was hitless in two at-bats. He was claimed on waivers from Toronto on March 31. Quiroz, 24, will have to clear waivers before the Mariners can send him to Triple-A Tacoma.
"He's firm behind the plate," said general manager Bill Bavasi. "He's a superior catcher and thrower. Offensively, he has some holes in his swing that need to be filled in."
Catcher Rene Rivera was recalled from Tacoma and joined the Mariners in time for Wednesday night's game. He had appeared in one game at Tacoma and had two hits in three at-bats. Rivera hit .195 (8-for-41) with four RBIs in Spring Training.
Rivera, 22, split last season between Seattle, Tacoma and Double-A San Antonio. A right-handed batter, he hit .396 with one homer and six RBIs in 16 games with the Mariners last season. In two Major League seasons, he is batting .357 (19-for-51) with a home run and six RBIs.
Harris sent down:
To complete the roster moves, right-handed pitcher Jeff Harris was optioned to Tacoma. He had no record and a 5.40 ERA in three games. Harris appeared in Tuesday night's 9-5 loss to the Indians, allowing two runs in 1 1/3 innings.
"It's disappointing," Harris said. "I wanted to stay here and contribute and help the team. All I can do is go down there and work hard."
Harris, 31, also split last season between Seattle, Tacoma and San Antonio. He was 2-5 with a 4.19 ERA in eight appearances (five starts). Harris made the Opening Day roster as a spring invitee.
The moves leave the Mariners with 11 pitchers.
"We really don't have a long man, but if the starters continue to pitch well that shouldn't be a problem," Hargrove said.
Richie Sexson appeared in his 1,000th career game Tuesday night. He made his Major League debut with the Indians on Sept. 14, 1997, as a pinch-hitter in a game against the White Sox in Chicago.
Head to head:
Facing lefty Cliff Lee didn't help Ichiro Suzuki on Tuesday. He was 7-for-17 lifetime against Lee going into the game, but was 0-for-2 with a strikeout and a walk on Tuesday.
The series ends Thursday with a 4:05 p.m. PT start. Hernandez (0-1, 1.80 ERA) faces right-hander Jason Johnson (1-0, 0.00 ERA).