Eleven minutes later, Bulgaria forward Martin Petrov raced through the Barcelona midfield with an explosive burst of speed to supply a perfect cross for Atletico striker Fernando Torres, who headed into the net at Vicente Calderon Stadium.
Kezman added the second in the 51st minute off a corner.
Atletico continued to pressure and Barcelona goalkeeper Victor Valdes was forced to make several saves, including two in the 64th.
Defender Pablo Ibanez was given a straight red card for a hard tackle on Eto'o.
Real Madrid also lost, falling 1-0 at Espanyol after defender Daniel Jarque scored the only goal.
Jarque raced forward to meet a free kick by Ivan de La Pena and referee Rodriguez Santiago appeared to blow his whistle for a penalty against the Madrid defense. But when Santiago saw the ball hit the back of the net he signaled a goal.
Santiago was then surrounded by Madrid players claiming the goal should be disallowed because the whistle had been blown before the ball crossed the goal line.
Madrid became more ragged after the goal, and in the 88th minute Madrid defender Sergio Ramos was ejected for a second yellow card.
Schalke was held to a 0-0 draw by visiting Hertha Berlin, keeping the team from winning its fourth straight match.
Schalke, expected to battle Bayern Munich for the title this season, turned in another poor performance against a sixth-place team that was down to 10 men after a 26th-minute ejection.
"The expectations are high here, but the reality looks different," Schalke goalkeeper Frank Rost said.
Also, former Germany coach Rudi Voeller made a successful debut as interim coach of Bayer Leverkusen, beating Duisburg 3-1.
For the second straight year, Schalke spent the most on new players in the Bundesliga, but the squad hasn't jelled.
Berlin controlled the match with the best early chances in front of 60,740 spectators at AufSchalke Arena. In the 10th minute, Marcelhino's free kick slipped through Rost's legs, but the 'keeper grabbed the ball before it crossed the line.
Berlin's dominance ended with the ejection of Brazilian midfielder Gilberto, who clapped at the referee while receiving a yellow card.
The draw left Schalke in fourth, six points behind Bayern after five rounds, and its likely to increase the pressure on coach Ralf Rangnick.
"The criticism is grotesque," Rangnick said, pointing out he led Schalke from a relegation spot to the Champions League last season.
Leverkusen ended its worst start in 23 years under Voeller, who lead Germany to the 2002 World Cup final and replaced Klaus Augenthaler on Friday.
Against the worst defensive team in the league, Leverkusen overcame a 31st-minute goal by Klemen Lavric to win.
Juan leveled on a header six minutes later, followed by scores from forward Dimitar Berbatov in the 41st and Athirson a minute from end.
Voeller, Leverkusen's sports director, said he had no plans to stay on as coach.
"This assignment will be short-lived," he said.
Leverkusen moved to seventh, while Duisburg tumbled into the relegation zone in 16th place.
Alessandro Del Piero scored two goals in his first start of the season, a 2-1 win over Ascoli that put Juventus into sole possession of first place in the Serie A after three matches.
Del Piero, reduced to a bench role by coach Fabio Capello in the first two games, converted a penalty in the 13th minute and then scored the match-winner in the 39th on a free kick. Ascoli defender Alfredo Cariello had equalized in the 32nd.
RSS