Carlo Ancelotti recognised Real Madrid had no answer to Kylian Mbappe in Tuesday's defeat to Paris Saint-Germain, acknowledging the match-winner was "unstoppable".
PSG claimed a slender 1-0 win over Madrid at the Parc des Princes to take a first-leg lead to the Santiago Bernabeu next month.
Mbappe got the decisive goal right at the end, skipping between a couple of defenders before firing through Thibaut Courtois' legs.
But Mbappe had terrorised the Madrid defence throughout, managing seven shots in total, drawing some vital saves from Courtois.
Mbappe also won the penalty that Lionel Messi had saved, with the France striker rising to the occasion against the club many expect him to join at the end of the season.
Ancelotti has rarely shied away from declaring his admiration for Mbappe, and he saluted the 23-year-old's show-stopping display.
"Mbappe is unstoppable," Ancelotti was quoted as saying by Marca.
"We have tried to control him. [Eder] Militao has done very well but [Mbappe] can always invent something out of nothing, and he created at the last minute."
In contrast to Mbappe's, Madrid's performance was significantly lacking in purpose, almost appearing to play for a draw from the outset.
They failed to get a shot on target for only the second time in a Champions League game since Opta records began (2003-04).
In fact, their 0.14 expected goals (xG) is Madrid's worst in a Champions League match since registering just 0.05 xG against Borussia Dortmund in April 2013.
Lack of attack
Explaining their issues, Ancelotti continued: "We've done quite well in defence but we haven't been very aggressive.
"We lacked something with the ball, we've missed many passes and it took a lot to get out of their pressure.
"[Marco] Asensio and Vini [Vinicius Junior], [Karim] Benzema as well, they didn't get many balls. With the ball we didn't do as we wanted.
"We tried to start from the back but it didn't work out. The low block had to be more aggressive, but it wasn't a conservative approach. It didn't work out for us, getting the ball as we know."
Benzema was withdrawn in the second half after making his comeback following over three weeks on the sidelines with a hamstring injury, though Ancelotti assured he was not substituted due to that problem.
"Benzema's problem was not physical," he said. "I changed him just before the end, the problem is that the balls we wanted did not reach him.
"I'm optimistic, although we have to do better in the second leg. We have the game at home and we don't have to worry about the away goal.
"It's clear that PSG have a good advantage but hopefully it won't be enough."
