With Arsene Wenger understandably resting many of his regulars following an intense mid-week Champions League clash with Barcelona, the Gunners once again failed to impose their will on a team that plays their football two levels down from the Premiership in League One.
Though Arsenal should have the quality to comfortably pick apart Leyton Orient, the in-form home side did their best to frustrate the Gunners all game to earn a highly-valuable draw at Brisbane Road.
The Gunners had gone ahead on a surprising header goal from stand-in captain Tomas Rosicky in the 54th minute, but Arsenal were unable to pad their lead, allowing the opportunity for the late equaliser by substitute Jonathan Tehoue in the 88th minute. Leyton's hero turned in a brilliant individual effort to beat Kieran Gibbs and Iganasi Miquel before firing his shot through Manuel Almunia to thrill an ecstatic home crowd.
Leyton earned themselves a hard-fought point and a trip to North London for a critical fifth round replay at the Emirates.
Despite the obvious gulf in class and positions within the framework of the English footballing structure, most would not have known from the on-field results.
Arsenal dominated much of the possession throughout the match, but as they often do, struggled to turn that into a decisive lead.
Many of the Gunners' issues had to do with a frustrating lack of danger produced by their trio of forwards, Andrey Arshavin, Marouane Chamakh and Nicklas Bendtner. Though the three men did create 14 shots between them, with 7 of them on goal, most of the efforts ever truly challenged Leyton keeper Jamie Jones.
With regulars Cesc Fabregas, Robin van Persie, Jack Wilshere, Samir Nasri and Theo Walcott rested for the match, Arsenal's attack lacked some of the bite that is usually present.
Arsene Wenger placed the onus of creating goal-scoring opportunities upon the previously mentioned attacking trio, as well as midfielders Denilson and Tomas Rosicky, and occasionally Alex Song.
While Arshavin did well to produce threats near the goal, Bendtner and Chamakh did little to justify more playing time with the Arsenal regular first team. Bendtner did pick out Rosicky's head with a well-placed cross for the goal, but otherwise, he was largely ineffective. Chamakh, for his part continued to look toothless in the goal area, clumsily passing the ball to the goal-keeper and pathetically stabbing at a clear-cut opportunity from point-blank range. He seems to have lost all of the confidence that his early success as a Gunner earned him.
The Cup squad continued its trend of playing down to the level of their opponents. Without being disrespectful to hard-working Leyton side, the Gunners did their best to keep their League One opposition in the game.
After being pushed to the brink by Championship team Leeds United and then once again by League One Huddersfield Town, Arsenal have failed to impress in their FA Cup matches the way that many would expect of the second-highest scoring team in the Premiership.
In a frustrating twist of fate, Arsenal forward Carlos Vela, on loan at West Bromwich Albion, scored the 92nd minute equalizer to earn his temporary team a draw in the Black Country Derby against Wolverhampton. Precisely the type of goal-poaching prowess that the Gunners missed at Brisbane Road.
Despite a 60 percent share of the ball possession, as well as a 20-7 advantage in total shots, 12 of which were on-goal, the Gunners were unable to find the back of the net again after Rosicky's header. Arshavin very nearly provided the 2 goal cushion the Wenger's men craved, but alas he pulled his shot just wide, as it glanced off the outside of the far post in the 84th minute.
Just before that effort, Leyton nearly earned the equalizer when forward Alex Revell blasted a point blank shot off of defender Sebastian Squillaci's face, prompting calls for a handball from many of the their squad.
Only six minutes later, 63rd minute substitute, Jonathan Tehoue made the home crowd's dreams come true as he burst past two defenders, slipping past Gibbs and Miquel, into the box, and blasting a low drive under Manuel Almunia.
Though Almunia may have done better to defend the shot, Tehoue's burst through the defense exposed the inexperience of Gibbs and Miquel, exploiting the young Gunners and evening the match.
To many Arsenal supporters, the result felt nearly inevitable, as confidence in much-maligned goal-keeper Almunia remains low, and any defense built around Squillaci always feels capable of leaking critical goals.
Overall however, the defense played solidly, turning away most of Leyton's opportunities without incident before the match-equalizing stunner.
With another goal from their 20 chances, the late effort from Tehoue would have been a moot point, offering Leyton only a morale boost. That was not to be, as Arsenal let their opponents' hopes linger late into the game, failing to put them away decisively.
In a period full of fixtures in four competitions, Arsene Wenger will not relish the return leg replay at the Emirates in a few weeks, but to Leyton's credit, they took full advantage of an Arsenal squad prone to occasional lapses.
Riding high off of their Champions League victory over Barcelona, Arsenal will not want to dwell on the negative aspects of their frustrating FA Cup draw, but they know full well that the result should have been very different than it was. With the replay scheduled for March 2 at Emirates Stadium, Arsenal will like their chances in a rematch with Leyton, but it's a match that should not have to be played. Especially with the Champions League return to Camp Nou looming just six days later.