Arsenal suffered a major setback in their Premier League title challenge as Gabriel Agbonlahor earned a 2-0 victory for Aston Villa at the Emirates Stadium.
Ashley Young had a first-half penalty saved by Manuel Almunia but then helped set up the opener when he crossed for Agbonlahor, who celebrated despite Gael Clichy appearing to get the final touch.
Agbonlahor then added the second 10 minutes from time when Villa broke, with Arsenal cancelling out the good work of last week when they beat Manchester United.
Since that victory Arsenal fans were given a glimpse of the future when Wenger fielded his youngsters in the Carling Cup, and the stars of tomorrow may be breathing down the necks of the current team following the type of defeat which has undermined Arsenal's recent title challenges.
Villa were played off the park by Chelsea during their last trip to London but there was no repeat and they should have gone into the interval ahead, regardless of Young's miss from the spot.
Arsenal's passing was sloppy and their attack lacked an edge while they had Nicklas Bendtner up front on his own, with Emmanuel Adebayor only on the bench after recovering from an ankle injury.
Carlos Vela and Aaron Ramsey were among the substitutes but there was no room for the precocious talent of Jack Wilshere. His time may be coming sooner than expected.
Wenger used his programme notes to highlight the speed of Agbonlahor and Young and they caused the hosts all sorts of problems, with a warning sign coming in the opening minute when Young fired straight at Almunia.
Brad Friedel fumbled a straightforward shot from Cesc Fabregas, with Curtis Davies required to hack the ball clear as William Gallas lurked, but apart from that it was Villa dictating play.
Young missed his penalty in the 20th minute after earning the spot-kick himself.
Mikael Silvestre had cleared only as far as Young after a deep cross caused chaos, with Theo Walcott sliding in when the Villa winger surged back in the box.
Almunia went the right way with the weak penalty but it still required a brave tackle from Gallas as Young chased the rebound.
Young may not have even been taking the penalty had Gareth Barry not been injured in the build-up, with Fabregas getting a yellow card for clattering into the England midfielder.
Villa were still taking the game to the hosts and former Arsenal trainee Steve Sidwell volleyed straight at Almunia.
Young almost atoned for his penalty miss with a drive that went just wide of Almunia's post, and he had another effort that went straight at the Arsenal goalkeeper after a mazy run.
Almunia was made to work harder when Agbonlahor pulled the ball back for Barry, the Spaniard down sharply as Villa threatened again.
Arsenal were struggling for fluency so Wenger made his move just after the hour mark, with Adebayor coming on to replace Abou Diaby.
Now playing a 4-4-2 formation, Arsenal appeared more threatening, although Wenger still looked frustrated on the touchline. Vela was the next to come on, replacing Bendtner, but it was Villa who took the lead.
Sagna was injured during the build up after falling awkwardly, with Villa raiding forward. Young crossed for Agbonlahor and the ball glanced past Almunia into his far corner as Clichy challenged.
Agbonlahor claimed it and there was no argument about the second when he chased a long ball, held off Gallas and fired home.
Arsenal manager Arsene Wenger suffered a miserable afternoon as his side suffered a defeat to Aston Villa that could have implications for their title bid.
"The performance was not good,'' Wenger said. "Top-level performances are about consistency and at the moment we are not consistent enough.''
Wenger felt play should have been called back for Villa's second. "It was a blatant foul on Carlos Vela on the edge of the box,'' said the Frenchman.
Wenger also bemoaned the fact the international break gives him little chance to lift a demoralised dressing room.
"Everyone is very down, it is a massive disappointment,'' he said, "Now I don't see them before Thursday or Friday, so I don't have [a chance] to pick them up.''
Villa boss Martin O'Neill was impressed by his side's performance and he too is
looking for consistency if they are to challenge for a place in the top four.
"I thought we were exhilarating,'' he said. "We were fearless. We have ability in the team, mark my words, it's getting them to believe they can keep going.
"You have to show a bit of character and determination after two defeats and I
thought that we showed that in abundance. The landmarks are to do with consistently performing. It was a great
performance but it's a tough old season.''
Villa are unbeaten at the Emirates Stadium in the three visits since it opened,
and O'Neill feels the quality of performance shows how they have progressed.
"The first year, we drew here in our opening game but we could have lost
35-1,'' he said. "Our progress since then has been fantastic We beat and drew with Chelsea last season as well. That doesn't necessarily
mean much because winning one-off games can only get you so far and it doesn't
mean we can win every week.
"But this will give the players great confidence, particularly in the way we
missed the chances but didn't let that affect them.''