Roma boss Luciano Spalletti has warned Roma players not to pick up "avoidable" cards after Thomas Vermaelen was sent off just 41 minutes into his debut against Porto.
The former Barcelona centre-back's first match for his new club ended prematurely on Tuesday when he picked up a second booking in the opening half of the Champions League play-off first leg in Portugal.
Roma had been leading at the time Vermaelen was given his marching orders thanks to a Felipe own goal, but had to settle for a 1-1 draw after Andre Silva equalised from the penalty spot in the second half.
"A player of Vermaelen's experience should not have got that first yellow card, but the second was more understandable," Spalletti told Mediaset Premium.
"He should not have committed the first foul. For the second one, the striker was heading towards goal and he had to take a chance, which is what he did.
"After 30 minutes we had both centre-backs booked and considering the football we were playing and the way we were dominating, we absolutely cannot be in that situation.
"We received cards that were avoidable and put us under extra pressure throughout the game.
"We gave the ball away too much towards the end of the first half after we had taken the lead.
"We were trying to force things a bit too much when we should have been looking to control the game. Instead, we forced the situation and an experienced team like ours cannot do that."
On the whole, though, the performance and result pleased Spalletti as the tie remained in the balance going into next Tuesday's second leg in Rome.
He added: "I am very happy with the performance. It was the first official match of the season and a pleasure in general to see them on the field. We battled from the off at a hostile ground.
"We started very well, always played the ball, fought hard and I really liked the team. We stayed compact after Vermaelen's sending off when we had to re-organise ourselves.
"I knew I had a strong side and I got confirmation of that."