DARLINGTON, S.C. -- Jimmie Johnson's status as a four-time defending Cup champion doesn't mean he's immune to the sometimes painful whims of Darlington Raceway.

Johnson suffered his third DNF of this season when he found himself in the wrong place at the wrong time Saturday night, up against the wall when A.J. Allmendinger shot backward up the track. Allmendinger T-boned the No. 48 hard on the driver's side, leading to substantial damage that knocked Johnson out of the race.

The crash on Lap 180 capped a trying night for Johnson, a former Darlington race winner who slapped the wall once early in the race and then bounced off Martin Truex Jr. in a later chain-reaction accident started when Greg Biffle went sideways and the drivers behind him slowed down. Johnson's team had repaired the right-side damage from that latter accident and gotten the No. 48 car back on the lead lap before the incident with Allmendinger ended their evening.

Allmendinger said he had been suffering brake problems over the last few weeks and was "out of brakes" when he slid up into the No. 48 car.

"The brake rotor exploded," he said. "The last 40 or 50 laps we were struggling with brake problems and just no brakes. We took all the brake cooling off and thought maybe we were going to fix it, and when that yellow came out I went to hit the brakes to slow down and the brake rotors exploded. I'm not sure which one, but I was just trying to aim for the bottom and try to miss everybody. I'm sorry to Jimmie. It wasn't his fault, but I had no brakes and couldn't do anything about it."

Johnson said over the radio that the crash knocked the wind out of him. Both drivers were examined at the infield care center and released.

"I didn't see where he came from," Johnson said. "All I know is that at the last minute, I saw a green bumper and it was a hard hit. Unfortunately we had all kinds of issues tonight ... but still had a very fast race car, and I think we could have salvaged a top 10, top five today. I'm going to go back and watch the video, because I have no clue. I guess it was A.J., because he came and apologized to me and said his brakes failed or something. I don't know if he was behind me or where he was, but he came in behind me and hit me hard."

Prior to that accident, the No. 48 team appeared on the verge of salvaging something out of a difficult night. Johnson fell a lap down after the incident with Truex, but earned the free pass, and had his damaged right fender replaced over a series of pit stops. He restarted in 22nd, the final car on the lead lap, when the race went back to green.

"You're back to a race car driver now, bud," crew chief Chad Knaus told him over the radio. "The thing looks good."

But not for much longer. The crash continued something of a mini-slump for Johnson, who's won three times this season, but not in his last seven races, and fell out of the points lead two weeks ago after being involved in an accident at Talladega. Johnson's three DNFs already this year come on the heels of only one last season. Johnson had suffered only seven DNFs over the course of his four championship seasons combined.

A consolation? The next two points races are at two of Johnson's best tracks, Dover and Charlotte, where he has won a combined 11 times.

Related:
• Video: Johnson has rough night at Darlington
• Video: No. 48 crashes out
• Notes: Johnson looking to get back on track with spoiler