The Washington Redskins backup QB Kirk Cousins leads the team to their fifth straight win in a row to put them on top of the NFC East igniting playoffs hopes in the Washington region. (The Washington Post)

A week after making the big plays down the stretch in a memorable relief appearance, rookie quarterback Kirk Cousins turned his first NFL start into a personal showcase here Sunday. He threw for 329 yards and two touchdowns in leading the Washington Redskins to a 38-21 triumph over the Cleveland Browns.

Cousins helped put the Redskins on more secure footing in the NFC playoff race, and prevented the absence of rookie star Robert Griffin III from undoing the team’s season. But Cousins knows he’s still the understudy; he said he will step aside willingly whenever Griffin’s sprained knee heals enough for him to play.

“I told him whenever he’s ready to come back, it’s his,” Cousins said. “I’m just trying to help this team win and get to the playoffs. And fortunately, we took a step forward today.”

Cousins said he knew all week there was a “strong possibility” that he would start the game. But he didn’t find out for certain, he said, until the team’s quarterbacks meeting Saturday night.

“You’d like to be able to let the world know when you feel like you’re going to start,” Cousins said. “But I had to keep it quiet. I couldn’t tell my friends. To their credit, they went and got tickets anyway. . . . I said it was 50-50 all week. . . . And then [Saturday] night I texted my college coaches and a few friends. I tried not to text too many people. But I just said it is official.”

Cousins threw an early interception Sunday but persevered to throw touchdown passes of 54 and two yards to wide receiver Leonard Hankerson.

“He did great,” wide receiver Pierre Garcon said. “He did a lot of great things. He passed for over 300 yards. It’s his first start. He wasn’t rattled at all. He made plays with his feet and with his arm. That’s all you can really ask for.”

Said Redskins Coach Mike Shanahan, “I thought he stepped up and just got more comfortable as the game went on.”

Shanahan said he didn’t say anything to Cousins to settle down the rookie after the early interception.

“He’s got a lot of confidence,” Shanahan said. “You can see that in practice. I did not say anything to him. I just told the guys that we stopped ourselves a couple times with penalties. Just relax. He got out of the pocket on that quarterback keep and threw a perfect strike to Hankerson. Not a lot of guys can make that read. . . . He made a perfect throw. That kind of gets you started. We needed that play at that time.”

Cousins ran with the ball when necessary, accumulating 22 rushing yards on three carries. He was effective throwing on the move on designed rollouts. But he certainly is not Griffin’s equal in that part of the game. The Redskins basically scrapped their read-option running game.

“We basically were running our playbook from last year,” center Will Montgomery said. “That’s our base offense. This new option stuff is new this year.”

Cousins took over after Griffin was hurt last week to throw a touchdown pass to Garcon and run for a tying two-point conversion in the final minute of regulation of an overtime victory over the Baltimore Ravens at home.

“I had all the faith in the world in Kirk,” rookie tailback Alfred Morris said. “I never doubted him at all. Kudos to him. He did one heck of a job of going out there and playing and helping us get this win.”

Morris said he found out for sure that Cousins would be the starter “when I saw it on ESPN” Saturday night.

Cousins admitted to some pre-game anxiety, saying he would be “lying to you if I said there wasn’t butterflies.” But he welcomed the opportunity to start, he said. And, once more, he made the most of his chance.

“It’s a good feeling,” Cousins said. “I said to my dad [Saturday] night, ‘It’s either going to be the highest of the highs if we win or the lowest of the lows. There’s not going to be much in-between.’ We’re certainly feeling the highs right now. It’s a game that I’ll remember for a long time. If I die tomorrow, I can say I started a game in the NFL and we won. So it’s a good feeling.”

The fourth-round draft choice from Michigan State said he learned something about the demands of being an NFL starter.

“I’ve got a lot more respect for Robert, for Rex Grossman and what it takes to be a starter in this league,” Cousins said. “It will test your soul every week.”