Cardiff City manager Erol Bulut told BBC Sport Wales:
"It is important that players come on and change the game and change the result, but we need it in the league games not just the cup games.
"First half it was not exactly what we wanted to show, we played too slow, we thought too slow.
"Second half was much better, and we created chances to score. There could have been more goals today."
Bulut hailed Rubin Colwill as a great player but said the 22-year-old Wales international could be “much, much better” with some changes to his game.
Colwill helped his side to a 2-0 Carabao Cup first-round win over League One Bristol Rovers after slotting home a late second to add to Mark McGuinness’ 68th-minute opener.
Bulut said of the midfielder: “Rubin is a player who when you put him on for 20 minutes he tries to cram in 90 minutes. This he has to manage much better.
“He tried to chip the ball over the goalkeeper and those are the chances you have to take. It’s too relaxed and we have to score from these kinds of positions.
“He scored in the end and I’m happy he feels better. He is a great player and he can be much, much better if he changes a few things.”
Bristol Rovers manager Matt Taylor said:
"I am disappointed. I thought we created the best chances in the first half, the team was set up well but we have to be better with the ball and in our attacking moments.
"We are a little bit aggrieved because we thought it was a foul on Luke McCormack, they countered against us and we defended the set piece poorly.
"It was a little bit of a lesson for certain personnel in relation to those moments but I have to be honest I am disappointed."