The Robins dominated the chances but had to settle for a 1-1 draw after Jason Walker struck six minutes from time to cancel out Shaun Harrad's superb curling effort for the hosts.
"They have had one shot in the second half and it has gone in the back of the net," Yates said. "We've not marked properly. It's a disappointed dressing room because we've dominated the second half.
"It was never going to be the easiest of games. They came to frustrate us and had a lot of pace on the break. We dealt with it well and only when we conceded did we look under any sort of pressure.
"We played some decent stuff in the second half, scored a great goal and could have had a couple more. We are not going to play like Brazil and able to turn it on like a tap. We got better and better and I thought the substitutes made a difference.
"But we have to keep our discipline at set pieces. We shouldn't be conceding goals as soft as that."
Yates added: "I'm happy with most of the things apart from the goal. Scott Brown has had nothing to do in the second half apart from pick the ball out of the goal. We showed some quality in really difficult conditions."