London - Juventus was stunned by Lech Poznan's stoppage-time equaliser in a 3-3 draw, and defending champion Atletico Madrid lost 1-0 at Aris in the opening round of the Europa League group stage on Thursday.
Juventus, a two-time European Cup champion, had clawed back a two-goal deficit to lead 3-2 from Alessandro Del Piero's goal before Lech Poznan striker Artjoms Rudnevs completed his hat trick to clinch the point.
Manchester City enjoyed a smoother night in the other Group A match, with goals from David Silva and Jo earning a 2-0 victory at Red Bull Salzburg.
Four months after ending its 14-year wait for a trophy, Atletico endured a miserable start to its title defense due to Aris midfielder Javito's second-half goal. Bayer Leverkusen routed Rosenborg 4-0 in the other Group B match.
In Turin, Lech Poznan scored twice in the opening half hour. Rudnevs found the net from the penalty spot after Brazil midfielder Felipe Melo brought down Slawomir Peszko, and he doubled the lead when left unmarked in the area.
Juventus pulled a goal back on the stroke of halftime when Chiellini headed in Del Piero's free kick.
The pair linked up again for the Italian team's second, with Chiellini scoring from close range after being left unmarked to receive Del Piero's pass.
When Del Piero put Juventus ahead it appeared the game was over, but Rudnevs made the home side pay for its profligacy when he hit a long-range shot past goalkeeper Alex Manninger just before the final whistle.
Juventus travels in two weeks to Man City, which has made a disappointing start in the Premier League with one win out of four games but dominated against Austrian champion Salzburg.
Silva beat goalkeeper Gerhard Tremmel after connecting with Jo's pass in the eighth minute and Jo tapped the ball into the net in the 63rd after pouncing on the rebound from Tremmel's block of Carlos Tevez's attempt.
"We definitely look like a unit already but some stuff is down to luck," City defender Vincent Kompany said. "I think in three or four months we will be even stronger than we are now."
In Group B, Atletico striker Diego Forlan was marked out of the game and Aris went ahead in the 59th when Javito controlled the ball with his chest between two defenders before firing past goalkeeper David de Gea.
Levski Sofia edged Ghent 3-2 in Bulgaria in Group C, while Sporting Lisbon won 2-1 at Lille.
Sporting took the lead in the 11th minute when right back Abel ran 60 yards unchallenged and crossed to Simon Vukcevic, who charged into the penalty area and finished powerfully past goalkeeper Mickael Landreau.
Lille's poor defense capitulated again when forward Helder Postiga headed into the top corner in the 34th.
Lille striker Pierre-Alain Frau pulled a goal back with an opportunistic effort after Sporting's goalkeeper fumbled Eden Hazard's strike in the 57th.
In Group F, CSKA Moscow won 3-0 at Lausanne Sports, while Sparta Prague beat Palermo 3-2.
Dinamo Zagreb gained an early advantage in Group D by beating Villarreal 2-0, while FC Brugge drew 1-1 with PAOK.
In Group E, AZ Alkmaar defeated Sheriff 2-1 and Dynamo Kiev was held 2-2 at home by BATE Borisov.