The Merengues were given a tough test at the Stadio Diego Armando Maradona, going behind early on to the Leo Ostigard header after a corner.
Bellingham first set up Vinicius Junior, then scored the second himself to turn the game around by half-time.
There was controversy when a penalty was awarded to the Partenopei for Nacho’s handball, as it seemed to come off his shin first, converted by Piotr Zielinski.
However, their perfect record was maintained because Federico Valverde hit a screamer from distance that bounced off the crossbar and in off the back of Alex Meret’s head.
“It was a tough game, hard-fought to the last minute. We conceded an avoidable goal, but then started to play and create chances. The moment of suffering was the equaliser with a very debatable penalty,” Ancelotti told Sky Sport Italia.
“The rules say that it came off the leg, so generally these are penalties that are not awarded in the Champions League.”
Ancelotti opted to start Toni Kroos in midfield rather than Luka Modric for the third game in a row.
“The introduction of Modric allowed us to control the ball more and take home the victory in a very difficult arena. It seems absurd that it was credited as a Meret own goal, because Valverde had that stunning strike, we know he can do that.
“Valverde is an extraordinary midfielder who among his many qualities has this long-range shot. It doesn’t matter how many goals he scores this season.”
Bellingham has had a sensational start to his Real Madrid career, scoring eight goals in nine competitive games.
“What surprises about Bellingham is that he is 20 years old. He has a lot of quality, but also incredible maturity and character for his age. That is what is really surprising.”
In the Sky Sport Italia studio, Fabio Capello asked if Antonio Rudiger was man-marking Victor Osimhen.
“Yes, we tried to make it one-on-one against Osimhen, who was very dangerous. The defenders did not leave spaces behind them, we only struggled on crosses, because that is where Osimhen is incredibly strong.”
Real Madrid are now top of the group on six minutes, followed by Napoli and Sporting Braga on three, while Leonardo Bonucci’s Union Berlin are rock bottom with zero.
Union Berlin had been 2-0 up against Braga today only to capitulate in stoppages.