"This level is, what they say, the biggest jump besides the big leagues," he said.
Jump? Rosenbaum is soaring.
In his home-away-from-home outing Friday night, the Loveland, Ohio native struck out six over six scoreless innings as the Senators snapped a four-game losing streak with an 8-1 win at Akron.
Rosenbaum (5-0) struck out six while recording 11 outs on the ground. He threw 63 of 96 pitches for strikes.
"I ran into a couple of situations but worked my way out of it. My defense was outstanding and I was able to get ground balls when we needed them," Rosenbaum said. "I was able to get the ball in[side] tonight; it was cutting a little bit, and I was able to throw my off-speed when I wanted to. Luckily, they hit it right to my guys."
The 24-year-old left-hander enjoyed a post-victory dinner with his parents and others comprising a large Rosenbaum contingent that made the 3 1/2-hour drive to the game.
There's a lot to celebrate. Through seven outings this season, the 2009 22nd-round Draft pick ranks first in the Eastern League in ERA (0.71) and WHIP (0.71). He has a 33-4 strikeout-to-walk ratio over a league-leading 50 2/3 innings.
Rosenbaum, who also had success at Harrisburg after a midseason promotion last year, credited improved fastball command following one of his more sparkling outings this year: an April 18 complete game. He has gone the distance twice, putting atop that category as well.
Still, the former Xavier University standout is not among the Nationals' Top 20 prospects. He was ranked No. 23 by Baseball America entering the season, despite a 2.14 career ERA in the Minor Leagues.
Is he ready for a new challenge, perhaps a Triple-A debut?
"It's out of my control," Rosenbaum said. "If I have to stay here the whole year, I will."
Aeros starter Steven Wright (3-2) surrendered five runs on five hits over 3 1/3 innings.
Senators first baseman Tim Pahuta and catcher Sandy Leon each collected three hits; Leon doubled home two runs in the second and singled home another in the fifth.