Eric Bedard will take the mound for Seattle on Saturday, and Wakamatsu is undecided as to who will start on Sunday. Garrett Olson (3-4, 5.46 ERA), who was roughed up for seven earned runs in 1 1/3 innings on Tuesday in Detroit, will move to the bullpen where he experienced some success earlier this year.
Rowland-Smith has pitched in one game with the Mariners this season and went 3 1/3 innings without giving up an earned run on April 10 against Oakland. He is 5-3 with a 4.31 ERA in 56 1/3 innings with Tacoma.
On Wednesday, Rowland-Smith threw a short bullpen session to get ready for his Friday start. His promotion is due in large part to his consistent progression and improvement while pitching for Tacoma, Wakamatsu said.
"His velocity has been up and the improvement has been there," Wakamatsu said.
Bedard is being pushed back an extra day to give him an extended break, but also to give the lefty an opportunity to pitch against division rival Texas on July 30 in what is shaping up to be an important series for the Mariners.
"It gives [Bedard] ample time to rest," said Wakamatsu, who hopes to decide on Sunday's starter in the next couple of days.
Olson might give Seattle the left-handed arm out of the bullpen that the Mariners have been lacking for part of the season, Wakamatsu said. He has a 2.25 ERA in nine games as a reliever, allowing 14 hits and three walks in 12 innings. Olson has struggled this season as a starter, though, going 3-4 with a 6.24 ERA in 10 games with 21 walks and 26 strikeouts in 49 innings.
Wakamatsu said that Olson needs to get comfortable being aggressive on the mound without overanalyzing every at-bat.
"He might be [the lefty specialist] we could use," Wakamatsu said. "His stuff is good and we just need to get him to believe that. I hope he is as effective in the bullpen as he has been before."
The Seattle manager hasn't committed yet to how many pitchers he plans to have on his roster throughout the remainder of the year, and in fact, that number could fluctuate between 11 and 12.
"It's nice to have that [14th] position player because it gives us extra flexibility," Wakamatsu said. "We went through a stretch this year when we had 11 pitchers. That can put a toll on your bullpen."
Mike Scott is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.