Reliever Justin Thomas and infielder Luis Valbuena will join the Seattle Mariners in Texas today – but five more Tacoma Rainiers will be coming to the majors on Tuesday.

Catcher Rob Johnson and third baseman Matt Tuiasosopo will join pitchers Brandon Morrow, Mark Lowe and Jared Wells as the Mariners expand their September and take a longer look at what their farm system has produced.

For Thomas, Valbuena and Tuiasosopo this will be their first big-league opportunity.

"Young players always bring a lot of energy when they come up, whether they're playing regularly or just getting the chance to get their feet wet," manager Jim Riggleman said.

Morrow will start one game of the Yankees series this weekend at Safeco Field – his first big-league start after spending most of the last two seasons in the Seattle bullpen.

Lowe and Thomas will be used in relief.

Johnson will catch pitchers in the bullpen when not starting, and though he'll be the fourth catcher on the roster, the Mariners want to try and get him in a few games as the starter.

Tuiasosopo isn't likely to budge Adrian Beltre, but having him on the team gives Seattle a legitimate third baseman should Riggleman want to use Beltre as the designated hitter.

Similarly, Valbuena may get a little time at second base.