What happened? Did he aggravate his earlier hamstring injury? Did he hurt something else? No, as his teammates and coaches quickly realized, it was nothing of the sort. Early in the fourth quarter, Murray just got tired.
"Did you see that?" Cowboys running backs coach Skip Peete joked Thursday at the team's practice facility. "It was an exciting game to watch, but I told him he could have had 300 yards if he didn't get tired."
Ah, tough love.
In the week following Murray's record-breaking performance (he'd finish with 253 yards Sunday -- 16 more than the franchise's all-time mark, set by Emmitt Smith in 1993), the rookie's first big opportunity definitely has been recognized for its worth.
But it has also been tempered, even if overly deliberate, for the sake of making sure Murray's first big moment isn't also his last.
"He's a very humble guy," Peete said. "It's not something we really need to worry about with him. The guy broke records at the University of Oklahoma, and there are a lot of great backs that went through there.
"But everybody's level of greatness is different, and it's my job to help him find that level -- and ultimately reach it."
It's a fascinating accomplishment, really. Yes, it was against the league's worst run defense. But 253 yards is a huge number against any defense.
Because of an injury to Felix Jones, this turned out to be Murray's first big chance to see more repetitions in a game. He'd already shown flashes, but a hamstring injury hindered his early progress in training camp.
So Peete approached Murray before the game. He told him to be ready for more snaps.
"All of a sudden, it seemed like he was getting seven yards, getting eight, getting five, getting eight, getting 12, getting 13," the assistant said.
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By the time he'd reached 25 carries, Murray's total had eclipsed the record set by Smith. A whopping 253 yards for an average above 10 yards per carry. Although humble and hungry, not even Murray could remember running like this.
"I never thought in a million years I'd have a day like (Sunday)," said Murray, who was the Cowboys' third-round pick in this year's draft after a four-year career at Oklahoma. "I've never experienced a game quite like this before."
Here's the good news: Murray might just be with the ideal organization to channel his success into more of the same. He has the right people around him to help make sure he knows how to deal -- both mentally and physically -- with this type of breakout.
After all, in the same locker room, wide receiver Miles Austin experienced an eerily similar breakout when he caught 10 passes for 250 yards in his first start with the Cowboys in 2009. Like Murray, he cracked the lineup because of an injury to someone ahead of him. And like Murray, Austin also broke the team record.
"We don't like to compare players," coach Jason Garrett said. "But when a guy gets an opportunity -- Miles goes to Kansas City and breaks all the (single-game) receiving records, and then DeMarco breaks all the (single-game) rushing records -- it's impressive.
"It's something we preach on a daily basis. If you get one play or 70 plays, that's your opportunity to take full advantage of it."
Austin's continued success should be a motivating factor for Murray, since it isn't guaranteed. While Murray's big game puts him in an elite class of guys with 250 yards or more in a game (names like O.J. Simpson, Walter Payton and Adrian Peterson), there are also players in the group (like Mike Anderson and Jerome Harrison) who haven't been able to sustain that success for a multitude of reasons.
Murray also has other teammates who are helping him along. It is very clear tight end Jason Witten has become a mentor for Murray as well. The rookie said he literally mimics Witten's work habits down to intimate details.
"I even got all of the same supplements he got from Vitamin Shop," Murray laughed. "I'm going to be honest: I copy him. Just the way he carries himself on and off the field. The way he works hard. The way he's so focused on football and it's a business to him. He wants to win."
So far, by all indications, that has been Murray's biggest goal also. And he should soon be getting plenty of opportunities to help his team do so.
But nobody is fooled into thinking Garrett won't go back to Murray to see if he can continue to build momentum from his previous performance. No doubt, it was a massive day for the rookie. Now, it's time to find out if there's more inside of him.
"He ran the ball well, but there's more areas for him to improve," Peete said. "After the game, I told him, 'Tomorrow, I'm still going to be cussing you out like I always do.' He knows it, and he seems to appreciate it. That's not going to change."