The Spanish and European champions thrashed Osasuna thanks to Vinicius’s treble, while Jude Bellingham scored his first goal of the season for Los Blancos.
However Madrid’s superstar striker Kylian Mbappe failed to find the net again and has scored one goal in his last seven matches, while Brazilian duo Eder Militao and Rodrygo were taken off injured along with Lucas Vazquez.
Second-placed Madrid reigned in Barcelona’s lead at the top of La Liga to six points before the Catalans visit Real Sociedad tomorrow.
Ancelotti brought Rodrygo into the line-up after the Milan defeat, reverting to a 4-3-3 formation.
The Brazilian winger drew a save from Sergio Herrera but was forced off with a knee problem during an intense start to the match.
Militao was taken off on a stretcher before the half-hour mark holding the back of his right knee, after going to ground in Osasuna’s area.
The defender missed most of last season with a severe knee injury and with David Alaba, Aurelien Tchouameni and Dani Carvajal out hurt already, his departure was particularly bad news for Real.
Ancelotti replaced Militao with 21-year-old defender Raul Asencio, making his debut after progressing through the youth academy.
Despite the setbacks, Madrid took the lead in the 34th minute when Bellingham teed up Vinicus, who whipped home at the near post.
England international Bellingham, whose goals were vital for Madrid last season, broke his duck this campaign with a fine lob after Asencio played a fine long ball to send him running through on goal.
Vinicius netted his second after Real Madrid goalkeeper Andriy Lunin, in for the injured Thibaut Courtois, found the forward with a long ball and he rounded the goalkeeper to finish.
The Brazilian finished second in the Ballon d’Or voting despite being favourite to win the award at the end of October, losing out to Manchester City midfielder Rodri, but soon completed his second hattrick in four games.
Brahim Diaz won the ball back deep in Osasuna territory and teed up Vinicius for a simple finish to complete the rout.
After Vinicius was replaced in the final stages Mbappe could play in his preferred position on the left flank but was unable to find the net as his personal travails continued, even as Madrid’s abated.