Falcons rookie Darius Johnson was having the game of his life against the Saints as an audience on NFL Network watched.

And then he made a crucial error that assured that play, and not his highlights, was what they remembered.

The wide receiver’s fumble in the red zone cost the Falcons a chance at the go-ahead touchdown in the fourth quarter. The play loomed large after Atlanta’s 17-13 defeat late Thursday at the Georgia Dome.

The mistake overshadowed Johnson’s six catches for 67 yards, both highs for his young career.

“That’s not the reason we lost that game, the turnover, though it doesn’t help us win the game,” Falcons tight end tony Gonzalez said. “Shoot, Darius played well, outstanding. That’s the best game he’s had all year. He’s got a bright future.”

Johnson wasn’t selected in the draft out of Southern Methodist and was on the practice squad last month. At 5-10 and 175 pounds, Johnson is slightly built for the NFL and his baby face makes him appear even younger than 22-years old.

Circumstances have made Johnson an unlikely mainstay in Atlanta’s offense and he’s taken advantage of increasing playing time over five games. The fumble was Johnson’s first major setback and prompted his teammates to urge him keep up his confidence.

“That’s part of the growing pains of coming into your own,” Falcons quarterback Matt Ryan said. “I think you have to feed off the positives what he did tonight… . . It’s tough because when you are down there and you’re in an area where you feel like you can score some points, those (turnovers) hurt. All in all, I think you have to remember that he’s five games into it and he’s playing very well for us.”

Johnson’s fumble came at a crucial point of the game.

The Falcons, trailing 17-14, had a second-and-eight at the Saints’ 22-yard line when Ryan completed a short pass to Johnson. He appeared to have an opening to try for the first down and turned up field.

But Saints linebacker K. Dawson poked the ball from Johnson’s grasp and cornerback Corey White recovered at the 13-yard line. Johnson said he didn’t see Dawson coming.

“I should have had (the ball) tucked high and tight but he made a good play and knocked the ball out,” Johnson said.

The Saints didn’t score off the turnover but flipped the field and took more than six minutes off the clock.

Johnson also had a dropped pass on third down in the third quarter. He was open on a crossing route and had no defenders near him but Ryan’s pass bounced off his hands.

“That was a key play that I should have capitalized on,” Johnson said. “(The pass) was a little behind me but that’s a catch I can make. I just didn’t catch it.”

Before those two bad plays Johnson made plenty of good ones.

In the first quarter, Johnson had a 17-yard reception, forced a 31-yard pass interference penalty against White and had an apparent six-yard touchdown catch reversed on a replay review. In the second quarter Johnson had three catches for 43 yards, all of them resulting in first downs, during a drive that ended with a field goal.

“I played the best game I’ve played all year in the first half but we just didn’t come out on top,” Johnson said.

Johnson continued to play after the dropped pass and lost fumble. He appears to be entrenched as the third wide receiver behind Roddy White and Harry Douglas and ahead of more experienced teammates Drew Davis and Kevin Cone.

The Falcons have gotten more than they could have hoped for from Johnson and he’s in line to get more opportunities in spite of the big mistake Thursday night.

“Darius is a strong young man who has come a long way in a short time in terms of undrafted free agents,” Falcons coach Mike Smith said. “Plays like that are going to happen. Unfortunately, it happened at a very bad time for our football team but he will bounce back. The guys in that locker room will help him.”