Ulster came into the game having won each of their three previous matches, and easily maintained their 100 per cent record, inflicting Cardiff's second loss of the season.
And South African born back-rower Pretorius admitted it was a poor performance but could not fault the effort of his players in a game in which they were ultimately outclassed.
"I think it's a scoreline that looks a little worse in the newspaper to be honest," he said.
"There were a lot of times when we were in their 22 and we would spill the ball and suddenly they've run it down the other end to score.
"I think we went through the phases really well, we just need to stick to our structure and trust it. We're up against it because quick turnover leads to points unfortunately.
"I'd say there are some positives to take but we have to go back to the drawing board and assess what went wrong.
"I think all of us need to learn from here and see where we can go for next week.
"We knew Ulster were going to come here with a lot of pride because it was a very important match for them."
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