"It felt great -- I got those butterflies, like always," Mercker said on Thursday morning. "That was the one test. If you quit getting those, you shouldn't be here. It was like old times."
Mercker struck out first batter Kyle Snyder, who whiffed on a changeup. The next batter, Mark Reynolds, took a called third strike -- also on a changeup. Stephen Drew fouled off six two-strike pitches before he flied out to right field.
Three up, three down. Cincinnati was down, 5-3, at the time and came back to win, 6-5, in the bottom of the ninth.
"That was a perfect situation for him," Reds manager Dusty Baker said. "In his first time in, he threw the ball great. His breaking ball looked better against lefties. His fastball, they're not picking it up. I saw that in Spring Training."
The last time Mercker pitched was on Aug. 11, 2006, and he blew out his left elbow on his final throw. He then underwent Tommy John elbow reconstruction surgery and missed all of last season.
Mercker felt ready to return during the offseason, and the Reds signed him to a Minor League contract on Feb. 8 with an invitation to Spring Training camp. It came with no guarantees that he would be taken north, but Mercker quickly established himself as a legitimate candidate for a bullpen spot.
"He told me he didn't want anybody to give him anything," Baker said. "He wanted to earn it. If he didn't think he had the stuff to pitch in the big leagues right now, you wouldn't have to send him home. He was going to go home. You can sort of tell. There's a look in a guy's eye if he thinks he has it."
In seven Spring Training games, Mercker posted a 2.57 ERA. He didn't allow run over his last five appearances.
"After the first day [of camp], it felt like I never took a year off -- as far as the routine and the butterflies, the anxiety and everything," Mercker said. "It was more of an adjustment not playing than it was coming back. Basically, it's the only thing I've ever done since I was 18. To do it is normal. Not doing it is the adjustment."