Real Madrid produced a massive comeback victory over Villarreal to win the tie 3-2.
The Los Blancos were two goals down at half-time, but scored three goals in the second half of the game.
Speaking after the game, Ancelotti hailed substitute Dani Ceballos and Vinicius Junior as the game changers.
Ancelotti said: “Him and Vinicius changed the match, they brought quality and energy.
“They were the two decisive factors in turning the game around.”
Carlo Ancelotti also revealed what he told his players at half-time that changed the game.
He said: “That they had to wake up, we lost many duels. The early goal made us take more risks and they controlled the ball well and managed several counterattacks. The team was too open, we failed to press. In the second-half it was totally different.”