Romo threw for a franchise-record 506 yards and five touchdowns during the match, but his night ended in disappointment when he threw an interception that allowed the Broncos to go on and score a match-winning field goal as time expired.
Despite the mistake, Garrett insists that his side have plenty of faith in the 33-year-old, who he believes is an "outstanding player".
"We have an immense amount of confidence in Tony Romo. If you watched us play over the last six, seven years, I think anybody would recognize that," Romo told reporters. "We think he's an outstanding player. I think he showed that yesterday.
"Unfortunately it didn't end up the way we wanted it to for our football team, but you've just got to keep throwing fastballs and keep going, and Tony will certainly do that and our team will certainly do that."
The defeat left the Cowboys with a 2-3 record for the season going into Sunday's match against the Washington Redskins.