Madrid won when Bellingham fed Vinicius into the area and the Brazilian fired a deflected strike into the top corner.
“He is adapting very well to La Liga and our style, he is very good,” Ancelotti told reporters.
With six points from their first two games, Madrid moved temporarily top of La Liga, ahead of Valencia on goal difference.
Champions Barcelona, which drew their first game against Getafe, welcomes Cadiz away from Camp Nou on Sunday in their first match at the Olympic Stadium on the city’s Montjuïc hill.
Earlier on Saturday, Celta Vigo edged past Real Sociedad with a late goal from Oscar Mingueza to earn a 1-1 draw after the Galicians sent Ander Baranetexia ahead.
Athletic Bilbao bounced back from last week’s loss to Real Madrid to win 2-0 at Osasuna.