Kirk Cousins’s NFL debut came after fellow rookie quarterback Robert Griffin III left Sunday’s game with a concussion, and it was a mixed bag.

Cousins threw a 77-yard touchdown pass to veteran wide receiver Santana Moss to give the Redskins a fourth-quarter lead. But his day ended with a pair of interceptions thrown on the final two drives as Washington lost to the Atlanta Falcons, 24-17.

“It’s difficult,” Cousins said. “But you don’t sign up to play the game at this level not expecting it to be difficult. So the bottom line is I didn’t get it done the way I wanted to today. But what I have to look at, the perspective I’m taking, is I’m going to learn from it, get better. And I’m going to pick up things that are invaluable going forward.”

Cousins completed five of nine passes for 111 yards after entering the game late in the third quarter. The Redskins decided entering the season to make Cousins, a fourth-round draft choice in April out of Michigan State, their primary backup to Griffin, ahead of veteran Rex Grossman. That decision was put to the test for the first time Sunday, with Grossman on the team’s inactive list for a fifth consecutive game.

“It’s a growing experience,” Redskins Coach Mike Shanahan said. “I’ve got a lot of confidence in Kirk, too. We’ll see where it leads us.”

Shanahan declined to say if it is automatic that Cousins would start next Sunday’s game against the Minnesota Vikings at FedEx Field if Griffin is sidelined. The decision about Griffin’s playing status is out of the Redskins’ hands. Griffin, under NFL rules, must be cleared by an independent neurologist before being allowed to practice or play.

“We’ll make the decision that we think gives us the best chance to win,” Shanahan said of the potential choice between Cousins and Grossman. “We’ll sit back and make those decisions at a later time.”

Cousins had some eye-catching moments during the preseason, and he gave the Redskins a 17-14 lead with 12 minutes 24 seconds to play Sunday when he delivered an on-target deep throw to Moss after the wideout had gotten behind the Atlanta secondary.

“I applauded him coming into the game in the heat of the battle, keeping it close and stepping up and being a leader,” Redskins rookie tailback Alfred Morris said. “I had complete faith in Cousins and think he’s a great quarterback.”

But Cousins said he knew at the time that outcome was far from decided by Moss’s catch.

“I understand it was a long game,” Cousins said. “I kept saying to guys, ‘We’ve got to finish. We’ve got to finish. We have probably two or three more possessions left.’ So nobody was getting too high or starting to pat ourselves on the back. We knew we had a lot of work still to be done.”

After the Falcons got a tying field goal and then a go-ahead touchdown, Cousins threw his first interception when Atlanta cornerback Dunta Robinson left the receiver he was covering, wideout Josh Morgan, to grab a pass headed for tight end Fred Davis. After the ensuing drive stalled out and Atlanta had to punt, the Redskins got the ball back at their 20-yard line with 1:21 left. But Cousins, delivering a pass right before taking a hit, had his throw toward Moss intercepted by safety Thomas DeCoud.

“I think the first one, he could have dumped it over the middle,” Shanahan said. “The second one, our receiver got jammed down the field.”

Said Cousins: “Both of them were just trying to do too much. I’ll learn from it. I need to take the check-down. I need to take the three-yard gain and accept that. You get in a two-minute situation. You want to come back. You just want to do too much. I think I’ll learn from it and next time I’ll take the check-down.”