Victory means Real return to the top of the LaLiga table on 18 points from six games, two ahead of Barcelona in second.
Real returned to the top of La Liga table after their 4-1 victory.
Real Madrid manager Carlo Ancelotti won the best coach award.
Real will take on RB Leipzig, Shakhtar Donetsk and Celtic in the group stage.
The win also made their Italian coach Carlo Ancelotti the first manager to capture titles in each of Europe’s top five leagues — England, Spain, Germany, Italy and France.
"Everything went well for them while everything we did turned out badly," Ancelotti told reporters after his side's first defeat of the season.
The Italian replaces Zinedine Zidane, who left the La Liga club last month.
outhampton beat Premier League leaders Everton 2-0 at St Mary's Stadium as Carlo Ancelotti's side became the final club to lose a game this season.
Everton made it three wins out of three as they topped the Premier League after a 2-1 victory at Crystal Palace, won by a controversial penalty.
The Pole should have put Napoli ahead minutes later when compatriot Piotr Zielinski's cross found him unmarked in the penalty area but he headed wide.