Rosen orchestrated his final drive efficiently, marching the Cardinals 49 yards to the Seattle 27 with 1:55 left, but a Phil Dawson missed field goal attempt from 45 yards ended up costing the Cardinals, who fell 20-17 as Seattle kicker Sebastian Janikowski hit a 52-yarder as time expired.
"I felt pretty good," Rosen said. "Just wish we had won the game."
Rosen finished with 180 yards and a touchdown with no interceptions on 15-of-27 passing. He also ran for 13 yards in two carries, which, Rosen said, helped him get his legs under him.
"That kind of got me in the flow of the game a little bit in the sense of like, 'I belong here,'" Rosen said. "As the game went on, I felt more comfortable as the offensive line, as the game went on, they definitely got more and more comfortable and started chipping away at their defensive line."
Rosen drew praise from his coach and teammates for his poise through the good, bad and ugly Sunday.
Coach Steve Wilks called Sunday a "very disappointing loss and that's an understatement," but said the bright spot was Rosen. Wilks repeated what he has said in the past about Rosen: He's poised. He's confident. He's athletic. He's smart. "It's not too big for him," Wilks said.
Right tackle D.J. Humphries walked out of the locker room Sunday "very impressed" by Rosen, especially how he handled himself.
"That's Josh. That's how he rolls. He's a gamer. He's one of those guys. Half the NFL is scared. Some guys are wired like that. Josh don't have that bone in his body. To watch such a young guy come in on such a big stage and his first start a divisional game, and watch him perform like he did is impressive."
Rosen's first career touchdown pass came at an ideal time: in the fourth quarter with Arizona down seven.
Rosen had what he called "almost an hour" in the pocket, waiting patiently for the routes to develop. He found second-year receiver Chad Williams for a 22-yard touchdown, putting the ball low, only where Williams, with coverage draped all over him, could get it. That tied the score at 17, giving Rosen a chance for a comeback win in his first career start.
"It was great," wide receiver Larry Fitzgerald said. "You could see how excited he was and that was a heck of a throw."
Rosen showed off his poise and maturity behind center all game while displaying an arm that made him what many pundits considered the most NFL-ready quarterback in the 2018 draft class.
He didn't take long to call audibles and checks at the line of scrimmage, lining up the offensive linemen how he needed them.
"I thought he played well," Wilks said. "I thought he gave us the opportunity and chance to win at the end. Great job with the operations and the two-minute situation."
But Rosen's best pass of the first half didn't count.
He hit Williams with a perfectly thrown ball that went over and past two Seattle defensive backs for what was initially called a 27-yard touchdown. But a review showed Williams was out of bounds and the play was reversed. Other times in the first half, Rosen didn't get much help from his receivers, who had at least three drops in the first two quarters, including one each by J.J. Nelson and Christian Kirk that could've led to touchdowns.
"He really did a great job of digesting what they were giving us defensively," Fitzgerald said. "I'm really happy with the way he performed."
"My decision," Wilks said. "Nothing detailed. I just felt, again, making the best decision for the team, I wanted to make sure that Mike (Glennon) was up if anything happened so that was it."
Rosen finished the first half with 50 yards on 6-of-13 passing and Arizona led 10-7.
Rosen's first snaps gave him his "Welcome to the NFL moments."
Rosen didn't bask in his first start. At his postgame news conference he was more bothered by the loss than excited about the moment.
"It was kind of like, binarily, I wanted to win the game," he said. "I didn't care if I threw 10 picks. I'd prefer that and a win over what happened today."