They were the first goals Portsmouth had conceded in 636 minutes of npower Championship football.
"We were the better team in all departments", said Pompey boss Cotterill. "I couldn't be more pleased with the way we played. Sometimes things go against you in football and we accept it and we will again.
"There was a clear offside in the build up to City's second goal and then one of our defenders ends up putting a cross into his own net.
"I was pleased with the way we passed the ball and we can take so many positives from the game.
"Bristol City are a good side and Keith Millen has done a terrific job here so it is not an easy place to visit.
"Despite that, we dominated the game and the only difference between the teams were the goals. If we keep playing that way we will continue to pick up decent results."
Winning boss Millen said: "I reckon one more win will see us safe now in the Championship and we are still aiming to finish in the top half of the table.
"It was our fourth successive win and a reward for determination and hard work against a very good side with many talented individual players.
"We were a bit open to begin with, but made one or two adjustments after which Portsmouth caused us relatively few problems.
"It was an absolutely brilliant goal by Albert Adomah and perhaps it was always going to take that sort of strike to get through a defence who had gone so long without conceding."