Trabzonspor marked its Champions League debut by upsetting Inter Milan 1-0 on Wednesday night, while Manchester United and Manchester City were held to draws.
Czech defender Ondrej Celustka scored a 76th-minute goal for Trabzonspor, which qualified for the competition only because Turkish rival Fenerbahce was removed while the club is probed for match-fixing.
United, which lost to Barcelona in last season's final, rallied for a 1-1 tie at Benfica in Group C on Ryan Giggs' stunning equalizer in the 42nd minute, a left-footed drive from the edge of the penalty area. Oscar Cardozo had put the hosts ahead in the 24th.
Aleksandar Kolarov's 74th-minute free kick gained City a 1-1 draw at home against Napoli in the English team's first match since 1968 in Europe's top club competition. The visitors, in their first match in the competition since 1990, had gone ahead five minutes earlier on a goal by Edinson Cavani,
Four-time winner Bayern Munich won 2-0 at Villarreal in the other Group A match on goals by Toni Kroos and substitute Rafinha.
Nine-time champion Real Madrid opened Group D play with a 1-0 victory at Dinamo Zagreb despite playing the last 17 minutes a man down after Marcelo's ejection. Angel Di Maria scored in the 53rd.
Ajax was held to a 0-0 tie by Lyon in the other Group D game. CSKA Moscow, in Group B with Inter, rallied from two goals down to draw 2-2 with French champion Lille. Basel beat Romania's Otelul Galati 2-1 in Group C.
Inter's defeat adds pressure on new coach Gian Piero Gasperini, whose team lost 4-3 at Palermo in its Serie A opener on Sunday.
"It's difficult, without a doubt," Inter goalkeeper Julio Cesar said. "In a moment like this we all have to stay together, work hard and find our way out of this situation."