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09/01/08 8:03 PM ET

Mariners roster swells, more on way

Thomas to be used vs. lefties; Valbuena to play second

ARLINGTON -- The first of two rounds of September promotions occurred on Monday.

Right-handed pitcher Justin Thomas and second baseman Luis Valbuena were in uniform for the Mariners' series opener against the Rangers in Arlington, and five others, including third baseman Matt Tuiasosopo, are scheduled to arrive in time for Tuesday night's game.

The Tuesday arrivals also include starting pitcher Brandon Morrow, who will make his much-anticipated starting debut this weekend against the Yankees at Safeco Field, catcher Rob Johnson, and pitchers Mark Lowe and Jared Wells.

Thomas, Valbuena and Tuiasosopo are getting their first taste of the big leagues.

"I wasn't expecting this," Thomas said. "I was called into [Tacoma manager Daren Brown's office on Saturday night] and he started talking about winter ball. I was supposed play in Venezuela. and he asked why I wanted to play there and I said I had heard the competition was better down there [than the Arizona Fall League]. There are a lot of Major League hitters there, so I thought it would be the best way for me to get ready for Spring Training."

Brown, who will manage the Peoria Javelinas in the AFL, kept the conversation going, before dropping a bombshell.

"He said, 'I know another place where you could face even better competition.' I knew he would be managing in the Arizona Fall League and thought that's what he was talking about, but then he mentioned Seattle and said I would be joining the team in Texas on Monday. I was just kind of stunned and shocked because I wasn't expecting it."

Thomas and Valbuena received early wakeup calls Monday morning for their trip from Seattle to Dallas, arriving in the early afternoon. They went directly to Rangers Ballpark in Arlington and prepared for their first night in the big leagues, not exactly sure when they would make their Major League debuts.

But both will have roles.

"With Thomas, we hope to use him as a left-on-left guy, the way we used Arthur [Rhodes]," manager Jim Riggleman said. "We want to see if there is something in his delivery that makes it tough on left-handers. Arthur was so effective against left-handers. [Cesar] Jimenez is more of a pitcher, more so than a specialist, and [Jake] Woods has done OK in that role, but he has been more of a pitch to both right and left hitters and has not really nailed down left-handed hitters.

"We need to find somebody who can nail left-handed hitters for us."

Riggleman said he hopes there will be some situations during the final month of the season and possibly during this series, that he could bring in Thomas to face a tough left-handed hitter -- like Rangers star outfielder Josh Hamilton.

Valbuena figures to get most of his playing time at second base.

"He has impressed everybody in the system, first at Double-A West Tennessee and then at Tacoma," Riggleman said, "so we're going to give him some playing time and evaluate his skills. This will give him a chance to get the butterflies out, so if he's here in the future, he would be more acclimated."

The scouting report on Valbuena, according to Riggleman, indicates that "he's a good ballplayer. He's not a burner on the basepaths or has explosive skills, but he's an all-around ballplayer."

The return of Morrow as a starting pitcher ranks high on the list of questions that the team hopes will be answered in September.

A late-inning reliever during his two seasons, Morrow was sent to the Minors on Aug. 5 to build his arm strength necessary for a starter. His final start for Triple-A Tacoma went superbly, as he allowed no runs and one hit over six innings Sunday afternoon and most likely will be on the mound Friday night against the Yankees.

Next to Morrow's insertion into the starting rotation, the play of Tuiasosopo could be a must-see when he spells Adrian Beltre at third base during the final month of the regular season.

It's a story of local boy makes good.

The 22-year-old turned down a football scholarship from the University of Washington three years ago after being selected in the third round by the Mariners in the First-Year Player Draft. He has methodically been working his way through the Seattle farm system, batting .282 with 13 home runs and 73 RBIs this season.

Tuiasosopo grew up in Woodinville, Wash., located northeast of Seattle, is the son of former Seahawks defensive lineman Manu Tuiasosopo and brother of former Huskies quarterback Marques. The Mariners prospect was a three-sport star at Woodinville High, as a quarterback in football, shortstop in baseball and guard in basketball.

Three of the players to be recalled have seen duty with the Mariners this season. Lowe was sent to Tacoma on Aug. 25, but did not pitch for the Rainiers, who ended their season Monday.

Wells has been promoted twice previously, appearing in one game.

Johnson, a September callup last season -- he went 0-for-3 -- becomes the fourth catcher on the roster and is being promoted primarily as a reward for having a solid season at Tacoma, where he batted .302, hit nine home runs, drove in 48 and was selected on Monday to the All-Pacific Coast League team.

The league selected 13 of its best players for the roster and will reveal its individual award winners later this week.

Johnson finished with a flourish, hitting safely in 33 of his last 38 games, batting .377 with 26 runs, 10 doubles, five home runs and 25 RBIs. Valbuena had a career-high 13-game hit streak, batting .436 (24-for-55) in the stretch with 12 runs, three doubles, four RBIs and six stolen bases.

Thomas started the season with West Tennessee and is 2-1 with a 3.71 ERA in seven games since being called up to Tacoma.

Also joining the team on Monday were coaches Pedro Grifol, Seattle's coordinator of instruction in the Minors, and Peoria pitching coach Gary Wheelock. They will stay with the club for approximately two weeks.

Jim Street is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.