Dak Prescott's throw to a tightly covered Michael Gallup had found its target down the sideline and put the Dallas Cowboys in position inside the 20 to kick a tying field goal with 21 seconds left Sunday night against the Los Angeles Rams in the debut of SoFi Stadium.

But there was a flag on the play.

Gallup had made illegal contact with Rams star cornerback Jalen Ramsey, according to the official, and offensive pass interference voided the 47-yard reception. Replays appeared to show fairly standard contact before Ramsey pulled his head and upper body back.

"I can tell you it was clear and obvious on the field, of a hand into the opposing player," referee Tony Corrente said in defending the call. "A full arm extension that created separation. In all situations that would be called. We're not going to allow that at any time of the game."

Mike McCarthy, making his debut as Cowboys coach, said he was surprised at the timing of the call and that Gallup and Ramsey were both hand fighting up the left sideline.

"I was surprised there was a call either way," McCarthy said. "Obviously I'm very disappointed in the call, especially that late. You don't see that at a critical part of the game."

Other Cowboys vehemently disagreed with it.

Ramsey felt equally strongly that it was the correct call.

"If they hadn't have called that, I would have been really upset,'' Ramsey said. "That was clear as day, in my opinion.''

Two plays later, Prescott's fourth-and-20 pass fell harmlessly to the ground as Dallas managed only 15 net yards on its final 10 plays of the game. The Rams held on to win 20-17.

"It was a huge chance,'' Prescott said. "We had a big two-minute drive at the end of the half. We were still able to move and get some progress, but we didn't get it done. But it is Game 1.''

Information from ESPN's Todd Archer and The Associated Press was used in this report.