Jose Mourinho lamented Chelsea's set-piece failings as defensive frailties lay at the heart of his team's latest setback at Porto.
A magnificent free-kick from William on the stroke of half-time in the Group G encounter at the Estadio do Dragao levelled matters after Andre Andre put the hosts ahead.
But, as in Saturday's 2-2 Premier League draw at Newcastle United, some slack marking from a corner allowed Porto captain Maicon to net decisively in the 52nd minute.
Danilo almost punished Chelsea further when he headed a similar chance against the post during the closing stages and Mourinho was frustrated as he told reporters afterwards how well-briefed his players had been on Porto's set-piece threat.
"We watch dozens and dozens of repetitions of Porto taking corners," he said. "We were completely ready for that and in a moment when the game is under control we concede a goal that is ridiculous.
"They hit the post from a similar mistake. Apart from that the game was balanced. Two ridiculous moments and we were punished.
"The most basic thing in football is a defensive set-play. The ball is there - you know the movement, you control the movements."
Mourinho maintained that overall he was happy with his team's performance.
Diego Costa was particularly impressive in attack and was involved as a handball shout against Ivan Marcano went unpunished.
Mourinho added: "We had chances after that to get a positive result and we had a clear penalty - so for me I am not here to criticise the players.
"The players reacted in a positive way and tried to play in a positive way.
"It's a difficult opponent, a difficult place to play. Champions League brings a different emotion to matches."
