Sometimes a decision taken for the best of reasons can deliver the worst of consequences.
When Arsene Wenger explained his choice to include Laurent Koscielny in a defence specifically designed to blunt the weapons of a renovated Chelsea, the logic made perfect sense.
This season's Chelsea, revamped by tens of millions of pounds of attacking reinforcements are faster, more precise with the ball, and far less dependent on physique.
Didier Drogba, the striker who won them the Champions League, has been allowed to leave for China. Opponents know they will be starting against Fernando Torres because that is what the club's owner wishes to watch.
Wenger's strategy? Rest his 6ft 6 ins, occasionally pedestrian, central defender Per Mertesacker and bring in Koscielny to counter Torres' pace and the creation of Chelsea's second attacking line.
"This defence is most adapted to their style of play," said Wenger ahead of kick-off. "Torres is going a lot in behind. Chelsea are a more mobile and technical side now with less impact players. It's a different opposition."
Fine idea, flawed execution.
Instead of blunting Chelsea, Koscielny helped the visitors into the home net. Torres out-muscled and thought the talented Frenchman for the opener, and probably should have drawn a penalty - and red card - from him a little later in the first half.
Eight minutes into the second, Koscielny's attempt to clear away a tidily placed Juan Mata free kick resulted in a winner that may ultimately be recorded as an own goal.
They were the key moments in a game in which the clubs traded clothes. Arsenal began evolving towards a counter-attacking side last season, with one of their most telling performances a 5-3 evisceration of a high-lined John Terry defence at Stamford Bridge.
With the rapidly adapted Eden Hazard, Mata and Oscar intermixing passes behind a central striker, Chelsea are now a team that relies on control of the ball to defend more than sheer physique.
Until the very last minutes of their 2-1 win, the visitors were ahead on possession.
"I don't know the numbers, but we could get the ball most of the time," said Torres. "And this is the best way to defend."
Though both clubs had conceded just six Premier League goals entering this fixture, each made ugly errors in conceding first-half goals. As they had fallen behind at Manchester City last week by poorly countering a set-piece, Arsenal conceded again here.
Mata's cross to the back post was regulation, yet David Luiz was allowed to run into yards of free space by Alex Oxlade-Chamberlain - a substitute for the injured Abou Diaby who did not seem to understand the midfielder's assignment.
Distracted by the Brazilian's liberty, Koscielny was shoved backwards and spun into a blindsided position by Torres. From there the Spaniard cleverly hooked a right foot around his marker's back to volley in.
Arsenal's riposte was delivered through an equally wide hole. As Oxlade-Chamberlain gathered possession on the right, Terry drifted towards a near post that appeared in little need of defending. Behind him David Luiz retreated to the six-yard box, allowing Gervinho room in between the central pair to collect his winger's cut-back cross, spin 180 degrees and pummel home.
Chelsea's lead was restored beyond repair when Thomas Vermaelen's charge upfield led to a tactical free kick some 35 yards from goal.
Mata curled it fast and hard across the face of goal, where Koscielny slid in to attempt a clearance. All the Frenchman achieved was a vicious deflection off a shin pad that Vito Mannone had no chance of parrying.
"It was one of the main targets we have this season - winning these kind of games," said Torres. "We want to be in the top four for sure and fighting for the title. Today was the first big test."
Petr Cech produced a wonderfully athletic twisting save to palm a nasty David Luiz deflection wide and the still wasteful Olivier Giroud spurned an added-time one-on-one. The points went back with the Premier League leaders; Wenger's sensible strategy failing on the day.
The Frenchman felt his side deserved at least a draw.
He said: "We conceded two soft goals from set-pieces. They had three shots on target and they scored two goals."
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