(CNN) -- Defending champions Inter Milan were held to a 2-2 draw by Dutch newcomers FC Twente in the opening round of the European Champions League group phase, while Barcelona put five goals past Panathinaikos.
Wesley Sneijder gave Inter the lead in the Netherlands with a powerful low shot, only for the Dutch champions to level through a Theo Janssen free-kick.
Twente took a surprise lead on the half hour mark when Diego Milito headed a Janssen corner into his own net.
But Inter drew level before half-time when Samuel Eto'o lashed home a right-footed shot from the edge of the area.
"The first half was very difficult but we did very well in the second, we controlled the game and I'm satisfied with the second half against a difficult team," Inter coach Rafael Benitez told reporters.
The other match in Group A, between Werder Bremen and Tottenham, also finished 2-2. The English club took a 2-0 lead in Germany after a Petri Pasanen own-goal and a header from Peter Crouch.
However, Bremen pulled a goal back before half-time through Hugo Almeida and equalized two minutes after the break when Marko Marin found the net with a low drive from outside the area.
Barcelona, winners in 2006 and 2009, went behind to Panathinaikos of Greece at the Nou Camp but hit back with two goals from world player of the year Lionel Messi and one from David Villa before half-time.
Messi missed from the penalty spot before Pedro added a fourth goal after 78 minutes and Dani Alves grabbed the fifth five minutes into stoppage-time.
Copenhagen of Denmark scored in the 87th minute through Senegalese striker Dame N'Doye to beat Russian side Rubin Kazan 2-0.
In Group C, three-time winners Manchester United could only manage a 0-0 draw at home to Scottish champions Rangers.
United manager Alex Ferguson made 10 changes to the team which drew 3-3 with Everton on Saturday, and the English club struggled to break down a stubborn Rangers defence.
Four long-range efforts from midfielder Darron Gibson were as close as United came to breaking the deadlock against the Scots.
"Rangers came out there and set their stall out to defend and you have to respect that," United captain Rio Ferdinand told Sky Sports. "At the end of the day we didn't lose. In the Champions League you've got to aim to get to 10 points, and we got one today."
The match was marred by a horrific injury to United winger Antonio Valencia. The Ecuadorian was carried off on a stretcher with a suspected broken ankle after a challenge by Kirk Broadfoot.
United's slip-up enabled Valencia to take control of the group after a 4-0 demolition of Turkish champions Bursaspor, who were making their Champions League debut.
Tino Costa, Aritz Aduriz, Pablo Hernandez and Roberto Soldado scored for Valencia, who were runners-up in 2000 and 2001.
French club Lyon, semifinalists in 2009, opened their 2010 campaign with a 1-0 home victory over Germany's Schalke.
Michel Bastos scored the only goal of the game in the first half, while Schalke had to play with 10 men for more than 50 minutes following the dismissal of Benedikt Howedes.
Finally, goals from Luisao and Oscar Cardozo gave Portuguese two-time winners Benfica a 2-0 win over Israeli debutants Hapoel Tel-Aviv.