Dak Prescott connected with Michael Gallup on a 47-yard pass during the Cowboys' final possession, which moved them into the red zone and field-goal range. However, it was nullified because Gallup was called for offensive pass interference.
"I was surprised there was a call there … particularly at that point in the game," head coach Mike McCarthy said, per Jon Machota of The Athletic. "You just usually don't see that (call) in a critical point in the game."
Gallup was battling with three-time Pro Bowl cornerback Jalen Ramsey in single coverage and extended his right arm while the ball was in the air. Still, it was fair to say Ramsey sold the call somewhat after he was beat for what would have been a massive play.
Ramsey said the penalty was "clear as day," per Emmanuel Morgan of the Los Angeles Times. "I would have been highly upset" if the officials didn't call it, the cornerback added.
Referee Tony Corrente defended the call after the game.
"I can tell you it was clear and obvious on the field, of a hand into the opposing player. A full arm extension that created separation," Corrente said to a pool reporter, per ESPN's Todd Archer. "In all situations that would be called. We're not going to allow that at any time of the game."
It ended up being one of the most important whistles of the game, as the Cowboys turned it over on downs two plays later.
Gallup finished with three catches for 50 yards as the Rams defense held a Dallas offense loaded with individual playmakers in relative check.
It was a disappointing Cowboys debut for McCarthy, who also coached the Green Bay Packers from 2006 through 2018. One of his decisions also came under scrutiny with the Cowboys facing a 4th-and-3 from the Rams' 11-yard line in the fourth quarter.
Rather than kick a field goal and tie the game, he elected to go for it. Rookie safety Jordan Fuller tackled rookie wide receiver CeeDee Lamb short of the first-down marker, and Dallas missed a key opportunity to score.
That call would have been long forgotten in the grand scheme of the start of the season for the Cowboys if Gallup was not whistled for pass interference and they scored on the final drive, but it stands out in the aftermath of a loss.