Undrafted rookie running back Robert Kelley (No. 22) led the Redskins with 40 rushing yards and a touchdown against the Falcons. (Brynn Anderson/Associated Press)

ATLANTA – Running back Robert Kelley had a difficult time processing the moment on Thursday. The Redskins’ undrafted rookie had just completed his first NFL preseason game and led the team with 40 rushing yards and a touchdown in the 23-17 loss to the Atlanta Falcons.

“It felt surreal getting out there for the first time in an NFL game,” Kelley said. “I don’t know. I can’t really explain it. It’s just a different feeling. I never thought I’d be here, so now I’m actually playing the game. I just went out there and played. I guess later on at night when I sit down, I’ll be really wowed by the fact that I played in an NFL game. It’s unbelievable to me right now.

“Growing up, you always hear people talk about the chances of you making it into the NFL is like the chances of you hitting the lottery. It’s just like a dream come true, and it don’t happen for everybody. You see people all the time that’s like real good and don’t get a chance to make it.”

The Tulane product was the fourth running back used behind Matt Jones, Chris Thompson and rookie Keith Marshall, but Kelley was the best player at the position. He broke off runs for 18 and 11 yards on a drive that ended with Kelley’s one-yard touchdown in the third quarter. It was the only moment in the game when the Redskins had an effective running game. They finished with just 79 yards on 24 carries.

“He smashes it up in there,” Redskins Coach Jay Gruden said of Kelley. “So he’s a big, physical back, and he’s definitely on our radar.”

Listed at 6 feet and 228 pounds, Kelley said he got all his jitters out on the opening kickoff with the return unit. He was used on special teams but felt it was an area that needed improvement after the game. Offensively, Kelley said he focused on his assignments and left the game with assurance in his ability.

“Just because I moved up to the NFL from college, the hitting is not harder but it’s just better players,” Kelley said. “I just feel more confident being able to make plays with NFL guys. I feel better about myself.”

More from The Post:

Redskins defensive snap counts vs. Falcons: Cravens shines

D.C. Sports Bog: Cousins is still trying to deflect attention

Ihenacho ditches his wrist brace in return to game action

Cousins is sharp in brief appearance in Redskins’ 23-17 loss at Falcons

Young linebackers stand out in preseason opener

D.C. Sports Bog: Best and worst from the loss to the Falcons

More: Redskins | NFL news | Camp schedule | Fantasy football

Follow: @MikeJonesWaPo | @lizclarketweet | @MasterTes