SEATTLE — Brandon Morrow's transition from Pacific-10 Conference baseball to the major leagues took all of eight games.

Morrow, a Cal product taken fifth overall by the Seattle Mariners in last June's amateur draft, was so impressive during spring training that he nailed down a spot on the opening day roster.

This after pitching just seven games for Seattle's rookie league team in Peoria, Ariz., last season and one game for Single A Inland Empire, a franchise no longer affiliated with the Mariners.

Seattle knew Morrow had a great arm coming out of Cal.

What he showed during the spring was that he also had the poise and maturity to play in the big leagues immediately.

"He came in throwing strikes," Mariners pitching coach Rafael Chaves said. "It's not a secret that he does have good stuff, and he won a job."

How prominent of a role he'll play in Seattle's bullpen remains to be seen. But the Mariners have indicated they may turn to Morrow, who brings a fastball in the high 90s, as a setup man for closer J.J. Putz. Seattle has two more experienced right-handers to share those duties, in Chris Reitsma and Julio Mateo.

Morrow first realized he had a shot to stick with Seattle after one of his early exhibition appearances against the Chicago Cubs, when he struck out Jacque Jones and Derrek Lee back to back, and then shattered the bat of Aramis Ramirez.

"That was really the first time I faced big league starting guys," Morrow said. "After that point, I really opened some eyes and thought I had a shot."

A Santa Rosa native, Morrow graduated from Rancho Cotate High before moving on to Cal, where he was named All-Pac-10 last season.

He had lots of loved ones to spread the good news to when he received word Sunday that he made the Mariners' roster.

"I was in the locker room, and you don't like to talk on the phone in the locker room, so I sent out kind of a mass text message, e-mail kind of deal," he said.

Morrow, who grew up rooting for the A's, came in and pitched a scoreless ninth Tuesday. He gave up a walk and a single but then retired the next three batters.

INJURY UPDATE: Pitcher Esteban Loaiza was diagnosed with a slightly bulging disk in his neck after being examined Tuesday by Bay Area back specialist Dr. Robert Rovner.

That diagnosis provides some clarity on a nagging injury that has bothered Loaiza since early in spring training. He began the season on the 15-day disabled list and is eligible to come off it Monday, but he won't be rejoining the rotation anytime soon.

According to A's assistant general manager David Forst, Loaiza is scheduled to resume throwing Tuesday but likely will need to build up arm strength before making a rehab start.

Before Tuesday's game against Seattle, manager Bob Geren said Chad Gaudin is likely to remain Loaiza's fill-in for the second cycle through the rotation. Gaudin will start Thursday against the Angels in Anaheim.

The news seems a little cheerier regarding right-hander Dan Haren. Haren said he was a little sore Tuesday after stumbling in his delivery against the Mariners on Monday. After the game he said he had "tweaked" his right hip flexor and might have over-reacted to the pain because he suffered a similar injury while training in the offseason.

But Haren planned to do his normal running Tuesday and said he should be able to throw his bullpen session Thursday and start Saturday in Anaheim.

ONE-HOPPERS: Geren repeated that he'll be cautious with shortstop Bobby Crosby's playing time for the first month of the season.

Crosby seems fully recovered from last season's lower back injury but missed most of spring training while working his way into shape. Crosby probably will sit out Thursday against the Angels, Geren said, and possibly Saturday's day game.

Geren slid Crosby from seventh to eighth in Tuesday's batting order, putting switch-hitter Bobby Kielty, who hits lefties especially well, in front of the shortstop. Kielty spelled Travis Buck.