Thibaut Courtois defended Chelsea goalkeeper Edouard Mendy after his error gave Real Madrid a two-goal lead in their Champions League quarter-final tie.
Chelsea had rallied after Karim Benzema's sensational quickfire double put Madrid 2-0 up at Stamford Bridge, with Kai Havertz responding shortly before half-time.
But the Blues' hard work was undone almost immediately after the interval, as Mendy's slack pass to Antonio Rudiger invited a challenge from Benzema, who was then able to fire into an open goal to complete his hat-trick.
It was Mendy's first error leading to a goal in the Champions League and only his third across all competitions in two seasons since joining Chelsea.
Although Chelsea had 57.3 per cent of the possession and 20 shots to Madrid's eight, the home side could not hit back again and now face a huge uphill task in the second leg in Spain.
Mendy at least had the sympathy of former Chelsea man Courtois, his opposite number in the Madrid goal.
"The problem if you make a bad pass as a goalkeeper is that there's no one behind, they steal the ball and score," Courtois said.
"He shouldn't be blamed, but a mistake by a goalkeeper is talked about a lot."
As much as 37.5 per cent of the game was played in Madrid's third of the pitch, but Chelsea created chances worth just 1.35 expected goals, even if Courtois would have been more comfortable with the visitors playing further upfield.
"We defended well," he said. "Maybe at times we were too deep and they took advantage of that to create chances. We have to improve on that and move the defensive line a bit higher up.
"We have to make sure we play well in the return leg."
Courtois should find a more supportive crowd in that return leg, having been jeered by the Chelsea fans on Wednesday in his first match back at Stamford Bridge in front of supporters.
The Belgium keeper left Chelsea for Madrid in a €35million transfer in 2018.
"Obviously it's a Champions League game, it's not a friendly," he said of the response.
"I didn't like how my departure from the club was explained, but I think I had really good moments at Stamford Bridge and I've got very fond memories of my time at Chelsea."