"What he has one time around, he has deception," Trembley said. "He'll use different arm angles, and he'll take something off. Boy, it's nice to have him out there. It was a big lift for our team."
Koji tossed nine of his 12 pitches for strikes and was pleased with where he was at.
"The pitchers and position players, they told me, 'Welcome back," he said through interpreter Jiwon Bang. "It felt really good."
Koji figures to get most of his time in the seventh or eighth inning, although Trembley said he would not rule out using the Japanese reliever in the ninth if current closer Alfredo Simon is not available.
Koji figures to get most of his time in the seventh or eighth innings, although Trembley said he would not rule out using the Japanese reliever in the ninth if current interim Alfredo Simon is not available.
"I probably wouldn't do that [Thursday] with Koji," Trembley said. "But if Simon has pitched a couple of days in a row, I would. But we've got to get to that point first, and I'm expecting that we will."
Koji was placed on the 15-day disabled list with a left hamstring strain on April 3 (retroactive to March 26), and after a pair of appearances at the team's Double-A and Triple-A affiliates, he was officially reinstated Thursday morning.
"I'm very, very happy to be here," he said. "I'll just prepare myself to be ready and throw wherever they want me to throw."
While Koji's hamstring is now 100 percent, he acknowledged the injury will still be in the back of his mind when he takes the mound. Uehara has a long history of hamstring issues, dating back to his playing days in Japan, and he made just 12 starts last year in his first season with the O's.
Koji pitched to a 1.69 ERA in six Spring Training games before exiting in the fifth inning of March 18's contest after he felt his left hamstring tighten up.
The Orioles hope limiting Koji to a one-inning role in the bullpen will help keep him healthy and productive. Baltimore is still missing regular closer Mike Gonzalez (strained left shoulder), who began a throwing program last week in Sarasota, Fla., but has not yet thrown off a mound. If there are not setbacks in Gonzalez's program, he could be activated by early June.