The Cowboys were in control for most of Thursday night's opener against San Francisco.
But a collection of reserves on both sides of the ball, many who won't be with the team when the regular season begins next month, failed to secure the victory.
"Man, you've got to finish,'' linebacker Jaylon Smith said. "No matter who is in the game, no matter what the score is, you've got to finish.''
The reserves gave up 14 points in the final 4:27 to turn what should have been a victory into a 24-21 loss. Head coach Jason Garrett and his staff will use it as a cautionary tale.
"It's a great learning experience for everybody,'' Garrett said. "A lot of our guys were not in the game who had been with us for a while. But every one of us can learn from that situation. How to handle it emotionally, how to handle it playing your technique and competing the right way at the end.
"Those guys were trying. But to make sure we execute in those situations and finish the game the right way.''