The right-hander threw 11 of his 15 pitches for strikes, mixing in several cutters that impressed catcher Matt Wieters.
"For the most part, it's breaking the right way and it has the right spin on it," Wieters said of the cut fastball Tillman has been tinkering with during camp. "It doesn't look like he's trying to make it do too much. It's definitely a pitch he should keep working on and could help him throughout his career."
Monday's outing also put to rest any lingering worries Orioles fans might have about Tillman's back. The 21-year-old was pulled out of his Feb. 21 workout early and missed his next scheduled bullpen session after suffering back spasms caused by falling asleep awkwardly on a couch.
"I've been 100 percent for the last two days," Tillman said. "I was even allowed to lift today. I think that's all in the rearview mirror, and we're going forward from here."
Arrieta opened up action for the black team and was also encouraged by his one scoreless inning.
"Everything I've worked on in the bullpen has really paid off," Arrieta said in terms of commanding his stuff at the knees. "[My] fastball was down; [I] only threw one breaking ball to [Miguel] Tejada, but it was sharp. A really good breaking ball; [it] felt good."
Arrieta's line mirrored Tillman's, as his lone blemish was a double by Cesar Izturis.
"I threw that one live [batting practice], but to get that 'L' screen out of the way and really face hitters pretty much for the first time felt good," Arrieta said. "It's nice to have people in the stands; it gives it sort of like an actual game feel. So I think everything went well for the first time out."
Besides Tillman, eighth-inning man Jim Johnson was the lone pitcher on the O's projected Opening Day roster who threw in Monday's game. Johnson said he used his one-inning stint as part of the orange team to help get the feel back for pitching in a real game.
"I was just trying to get in as many offspeed pitches as I could," he said. "Normally, that probably wouldn't be the case, but I was just trying to get a feel for things and get things progressing. It's usually the last thing that come around in the spring is your feel. Your arm strength is usually the first to come and then you progress through your pitches."
Johnson tossed a scoreless second inning, and his 13-pitch effort was singled out later by manager Dave Trembley.
"Johnson threw good," Trembley said. "Everybody got in. I liked [Brandon] Erbe."
Trembley said Erbe's ball had a lot of "late life" and that the scouting report on the right-hander, who has made significant strides in his delivery, was pretty accurate.
"He's what everybody has told me," Trembley said. "He's certainly a lot better than I saw at the Hall of Fame Game in 2007."