Johnson was sandwiched between two Trojans on a quarterback sneak for a first down late in the first quarter. He played one more series before his back began to stiffen up. He then became light-headed just before halftime and trainers wisely made him hang up his cleats for the night.
"It was real hard," said Johnson, who said he still had a throbbing headache after the game. "I wanted to (go back out), but they told me I had to because they didn't want me to move around since it was a back thing. So I just had to sit in (the locker room) and basically do nothing."
Johnson, making his third start, led two scoring drives by completing 8 of 16 passes for 91 yards. He threw a perfect strike to Marcus Monk on a fade pattern for a 12-yard touchdown that tied the score at 7-7 early in the first quarter.
It was one of several successful audibles Johnson called during his limited action.
"Robert has had three good games guys," said Arkansas coach Houston Nutt. "He has played really good, he has played hard and he's competing. He has made good throws, some beautiful throws. The touchdown, that was a check to Monk. We had a slant called and they rolled two (defensive backs) over to protect against it and they went to a fade."
With Johnson out, the Razorbacks were forced to go to back-up Alex Mortensen, a redshirt freshman whose only playing time came late in a 49-17 win against Missouri State in the season opener.
Mortensen bobbled his first snap late in the second quarter, but said he was more excited than nervous as he was thrown into the fire against the two-time defending national champions.
"I think the experience will help a lot," Mortensen said. "It's unfortunate the way the game went, but at the same time, it was good to get my feet wet and even learn from some of the mistakes I made. But it was good to see the defense and see the field and get hit again and mix it up a little bit."
Mortensen was sacked twice and completed just 4 of 10 passes for 38 yards. He also led a scoring drive against USC reserves that was capped by a five-yard touchdown pass to Monk in the fourth quarter.
Since the score was well out of hand, Nutt decided to stick with the ground game during most of the second half.
"Alex did some good things, but when they're smelling blood, it's tough," Nutt said. "They've got their ears pinned back and they knew we were going to have to throw. I just didn't want to put Alex in that situation."
Johnson expects to recover quickly and plans to be ready when the Hogs travel to Alabama on Saturday. He was encouraged by the things the offense did well early, including picking up six of its first seven first downs through the air.
"We all did pretty good," Johnson said. "We moved the ball really good. We just have to do more things on offense. We can't make any mistakes. We made good plays here and there, but we've got to be more consistent.
"I thought it was going to be a really good game after (the touchdown pass to Monk made it 7-7). We knew they were a good team, we just put everything on the table and went after them.
"But they're not No. 1 for no reason."
Mortensen Fills In After Johnson's Injury
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