With the Razorbacks leading 28-27, Tigers quarterback Bo Nix attempted to spike the ball and stop the clock on third-and-1 at the Arkansas 20, but instead he fumbled the snap. Nix picked the ball up and appeared to spike it backward, which would have resulted in a fumble.
The play was originally ruled intentional grounding, however, and that call was confirmed on review, leading to a loss of down and a 10-second runoff for the Tigers.
Auburn kicker Anders Carlson then came on and kicked a winning 39-yard field goal with 7 seconds left.
Arkansas coach Sam Pittman said afterward that he was told by referees that Nix did not throw a backward pass. But that's not what he said he saw from the sideline.
"The ball went backwards 6 yards," he said. "I saw a fumble and a spike that went backwards 6 yards."
The SEC said in a statement later Saturday that there is "conclusive video evidence" that Nix's pass was backward, but explained the ruling was not overturned "because recovery of the football was not clearly made in the immediate continuing football action."
"Both the determination of a backward pass and the immediate clear recovery are required to reverse the ruling on the field under Rule 12-3-2-e-1," the SEC said.
Arkansas athletic director Hunter Yurachek on Sunday said he spoke with the SEC office.
"I expressed my disagreement and disappointment with the final decision," Yurachek said on Twitter. "However, there is no further action to be taken and we will turn our attention to the Ole Miss game on Saturday."
Pittman, who was visibly frustrated, said he didn't want to pin the loss on one play. But he said Razorbacks players in the locker room were down and hurting.
"And they should," Pittman said. "They put a lot of sweat into preparing to play Auburn ... and they just had one more play."
Arkansas defensive back Jalen Catalon said he thought Nix threw the ball backward, too.
"We thought it was a fumble," he said, "but sometimes the game doesn't bounce your way. ... A tough one to swallow."
Auburn coach Gus Malzahn said one had to give Arkansas credit for how hard it battled.
Sometimes it's how you win, Malzahn said, but "these SEC wins this year are not easy."
Auburn, which improved to 2-1, is scheduled to go on the road to play South Carolina next Saturday. Arkansas, which fell to 1-2, is to host Ole Miss.