The England midfielder, who moved to Madrid from Borussia Dortmund in June, netted his sixth goal in six games this season.
"He has quality and it looks like he's lucky," the Italian told reporters at the Santiago Bernabeu.
"He's smarter than others when attacking from the second line. He has this quality and he's making the most of it."
"He's one of the best forwards in the world. He makes the difference. Vinicius will be back next Wednesday. We'll see if he makes it for Sunday (against Atletico Madrid)," Ancelotti said.