Storen threw eight pitches, inducing a foul popup, a flyout to center field and a groundout to first base. He threw five fastballs that sat at 92 mph, or 3 mph lower than his average during the 2011 season.
"Mechanics felt really good," Storen said. "The big thing for me wasn't velocity, necessarily, but I wanted to be down in the zone and sink my sinker, and I thought I did a good job doing that. I was happy with how everything went. I thought I was commanding the strike zone well."
Storen mixed in two sliders and a changeup, recording six strikes, one on a swing and miss.
"The offspeed stuff, that command is going to get there," he said. "I threw one changeup but I felt really good throwing that in live batting practice and [simulated] games.
"I'm not concerned with that, but I thought my ability to make adjustments from pitch to pitch was good, and I think that's a really important thing."
Last season, Storen went 6-3 with a 2.75 ERA in 75 1/3 innings for Washington. He tied for sixth in the Majors with 43 saves and converted 89.6 percent of his chances.
Washington manager Davey Johnson has said that Tyler Clippard, who is 13-for-13 in save opportunities since taking over the closer role in late May, will retain the job after Storen returns. Storen stated that while on rehab, he is "preparing to close, regardless," but understands Johnson's decision with the Nationals in first place.
"I've got to work my way back in that bullpen, because those guys have been throwing there all year and know what they're doing and there's no room for error in that situation, especially with how well we're doing," Storen said. "I totally get it 100 percent."
Infielder Chad Tracy joined Storen in the Potomac lineup, playing five innings at third base on the second day of his rehab from a torn right groin muscle he suffered on May 26.
Tracy, 32, went 0-for-3 with a walk and an RBI as a designated hitter Wednesday and 0-for-2 Thursday, although Frederick outfielders twice robbed him of hits, including on a fly ball to the right-field wall. He also fielded a sharp grounder to his left and started a double play.
"I've got a little ways to go. I'm not quite to where I'd like to be, but I feel like I'm getting close," Tracy said. "I'm still lacking a little strength in [the groin]. Running, some sharp movements, I still feel it a little bit, but it actually feels better today than yesterday, so that's a positive."
Tracy plans to stay with Potomac until returning to Washington after the All-Star break. He's hitting .265 with an .837 OPS (on-base plus slugging percentage), three home runs and 12 RBIs for Washington and is 6-for-18 with nine RBIs a pinch-hitter.