Premiership leaders Arsenal lost for the first time in 23 league games after goals from Stewart Downing and Tuncay Sanli handed relegation candidates Middlesbrough a vital 2-1 victory at the Riverside Stadium here Sunday.
Tomas Rosicky's last-minute consolation goal proved too little too late for an Arsenal team now just a point ahead of second-placed Manchester United, and facing up to its first crisis of the campaign.
Arsene Wenger's men surrendered this season's only unbeaten top flight record after failing to truly test the home team's rookie keeper Ross Turnbull and the Gunners have now taken just one point from the last six available.
With United and Chelsea gaining momentum going into the traditionally hectic festive period, the return of several first team regulars cannot come soon enough for the stuttering Londoners.
Arsenal's second trip to the north-east of England within the space of five days saw Wenger name an unchanged team, more by necessity than design.
Still missing key midfielders Cesc Fabregas, Mathieu Flamini and Alexander Hleb, the Gunners' French coach was forced to stick with the same starting 11 which had laboured to an unconvincing 1-1 draw at Newcastle.
That energy-sapping match had stretched Arsenal to their limit and a lethargic start suggested fatigue was still a factor. Within four minutes Arsenal were trailing and it was ex-player Jeremie Aliadiere who lay behind an unlikely early setback.
The Frenchman has struggled to make an impact at Middlesbrough following his pre-season transfer from the Emirates Stadium but a fine run took him clear of defender Kolo Toure.
Arsenal's Ivorian centre half was forced to foul his former team-mate inside Manuel Almunia's area and referee Howard Webb had no hesitation in awarding a penalty. Downing dispatched the spot kick with aplomb.
Those travelling Arsenal supporters expecting a swift response were sorely disappointed as Middlesbrough maintained their dominance.
Toure timed his second key tackle of the afternoon to perfection to deny Downing a clear run on goal and it was not until the 36th minute, when Togo international Emmanuel Adebayor headed an Emmanuel Eboue corner narrowly wide, that the Gunners threatened.
Tuncay should have doubled the Teessiders lead six minutes before the break only to flash a wild shot well wide.
In fact it was Gareth Southgate's side which continued to create the better chances and Tuncay had another glorious opportunity to extend the home team's lead in the 50th minute.
A strong run from the Brazilian midfielder Fabio Rochemback drew the Arsenal defence but Tuncay fired wiide with only Almunia to beat. And Netherlands midfielder George Boateng almost capped a flowing move with a stunning goal only to see his 60th minute shot flash wide of Almunia's right hand post. But Tuncay finally found his range 16 minutes from time to fire Boro 2-0 up after Almunia had failed to hold Gary O'Neil's fierce strike. When the Czech Republic international Rosicky drilled a right foot shot beneath Turnbull with the final kick of the game it offered cruel evidence of what might have been for Wenger's men.
-- English PremierSHIP results
-- Played on Sunday
-- Middlesbrough 2 (Downing 4-pen, Sanli 74) Arsenal 1 (Rosicky 90+5)
-- Bolton 4 (Scharner 3-og, Nolan 37, Davies 70, Anelka 89) Wigan 1 (Landzaat 14)
-- Tottenham 2 (Chimbonda 45, Defoe 83) Manchester City 1 (Bianchi 61)
Played on Saturday.
-- Manchester Utd 4 (Giggs 40, Tevez 45, 60, Ronaldo 90-pen) Derby 1 (Howard 76)
-- Aston Villa 1 (Barry 72-pen) Portsmouth 3 (Gardner 10-og, Muntari 40, 61)
-- Everton 3 (Yakubu 51, 61, 79) Fulham 0
-- Newcastle 2 (Martins 37-pen, Beye 90) Birmingham 1 (Jerome 9)
-- Chelsea 2 (Shevchenko 23, Lampard 75-pen) Sunderland 0
-- Reading 3 (Hunt 17-pen, Doyle 60, Harper 67) Liverpool 1 (Gerrard 28).