Real Madrid moved to the top of La Liga, level on points with rivals Atletico, after they won 3-0 at Cadiz, where Karim Benzema scored twice.
Karim Benzema's fine run of form continued with a double as Real Madrid won at Celta Vigo to move up to second place in La Liga.
Lautaro Martinez's late winner stretched Inter's winning run to eight games, while Cristiano Ronaldo answered his critics with a perfect hat-trick.
Serie A leaders Milan were stunned 2-0 by Spezia to give Inter the chance to leapfrog them, while Atletico Madrid went eight points clear in La Liga.
Real Madrid ended Atletico Madrid's 26-game unbeaten run with a 2-0 win at the Alfredo Di Stefano Stadium to move within three points of the La Liga leaders.
AC Milan restored their five-point lead at the top of Serie A with a 2-1 win at Sampdoria on Sunday.
Zlatan Ibrahimovic made a winning return to the AC Milan team as his quickfire double won the Milan derby, while Real Madrid and Barcelona suffered shock defeats.
Liverpool defender Nathaniel Phillips has been loaned back to Stuttgart until the end of the season, just 17 days after being recalled.