The Broncos powered into a 24-point lead just before the break, but scored only seven points in the final two quarters of the game and were forced to hang on as Colts quarterback Andrew Luck nearly brought his side back into the game.
"I don't think it was disappointment," Fox told reporters. "Like I told the team, you never make excuses for Ws in this league.
"It's hard to win in this league. You're competing against 31 other teams that are the best in the world at what they do. So you take it one week at a time, try to stay even keel, and we'll make the corrections. We'll learn from this."
Fox's side face the Kansas City Chiefs in their second match of the season tomorrow.