MILAN - Panathinaikos beat Inter 1-0 at the Giuseppe Meazza to send the Nerazzurri to their second defeat of the season.
But José Mourinho's men qualify for the round of sixteen with Matchday 6 still to play as Werder Bremen held Anorthosis Famagusta 2-2 away in tonight's other Group B fixture.
There were two changes to the team that beat Juventus on Saturday, with Luis Figo making his comeback from injury against the Greeks and Ivan Cordoba returning from suspension.
A first half of few chances saw Adriano crash on to the outside of the post after a deft through ball from Cambiasso, and Ibrahimovic toe punt on to the roof of the net after another pass from the Argentine midfielder.
Ten Cate's men took the lead against the run of the play 24 minutes after the restart when José Sarriegi converted from close range after Julio Cesar failed to hold a header from Goumas.
After bringing Quaresma on for Muntari at half time, Mourinho threw on Balotelli and Cruz in the closing stages and Inter created plenty of chances for an equaliser, with Panathinaikos keeper Mario Galinovic thwarting Adriano and Maicon before making saves from Cruz and Materazzi.
Inter 0-1 Panathinaikos (HT: 0-0)
Scorer: Sarriegi 69.
Inter: 12 Julio Cesar; 13 Maicon, 2 Cordoba, 23 Materazzi, 6 Maxwell (9 Cruz 75); 4 Zanetti, 19 Cambiasso, 20 Muntari (77 Quaresma 46), 7 Figo (45 Balotelli 72); 8 Ibrahimovic, 10 Adriano.
Subs not used: 1 Toldo, 5 Stankovic, 16 Burdisso, 33 Mancini.
Coach: José Mourinho.
Panathinaikos: 1 Galinovic; 29 Nilsson, 24 Vyntra, 8 Goumas, 3 Sarriegi, 31 Spiropoulos; 19 Gabriel (22 Tziolis 84), 23 Simao, 15 Gilberto Silva, 21 Karagounis (14 Salpingidis 63); 26 Mantzios (5 Rukavina 90+5).
Subs not used: 30 Tzorvas, 4 Mattos, 7 Ninis, 27 Ivanschitz.
Coach: Henk Ten Cate.
Referee: Tom Henning Ovrebo (Norway).
Booked: Galinovic 89, Goumas 90.