Real Madrid suffered a 3-2 defeat at home against Shakhtar Donetsk in their Champions League Group B opener on Wednesday.
The Ukrainian side raced into a 3-0 lead in the first half with a strike from Brazilian midfielder Tete, an own goal from Madrid defender Raphael Varane and a fine goal from Israeli forward Manor Solomon.
Luka Modric and substitute Vinicius Jr score Madrid's consolation goals in the second half.
Inter Milan were held to a 2-2 draw by Borussia Monchengladbach in the other Group B encounter.
Elsewhere, in Group A, defending champions Bayern Munich crushed Atletico Madrid 4-0 with winger Kingsley Coman scoring a brace, while Salzburg and Lokomotiv played out a 2-2 draw.
In Group C, Manchester City beat Porto 3-1 and Olympiakos overcame Marseille 1-0.
Meanwhile, in Group D, Liverpool edged Ajax 1-0 and Italian side Atalanta thrashed Denmark's Midtjylland 4-0.