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Olivier Giroud's winner came late, but it had been coming. Arsenal are into the next round of the FA Cup, probably the only trophy they have a realistic chance of winning, having been given one hell of an early scare by Preston.
The Championship club, having gone ahead though Callum Robinson, lived to regret not scoring more in their blitz of the first half hour. It was Aaron Ramsey's equaliser within the first minute of the second half that tilted the game's balance, even if it was not until the 89th minute that Giroud scrambled home to score.
Arsenal had fallen behind in the eighth minute. Preston midfielder Aiden McGeady pulled off a delightful pair of pirouettes to bamboozle Lucas Perez and then Ramsey as Arsenal's defence was opened up. Home fans made loud claims for a penalty when Nacho Monreal clattered Jordan Hugill, but indignation turned to celebration within a split second. The ball had spilled to Robinson to slot home.
Arsenal's defending was lumbering and circumspect, just as it had been during Tuesday's 3-3 Premier League draw at Bournemouth. Shkodran Mustafi again looked off the pace in the centre, though he did perform a fine block of a goal-bound header in the 22nd minute.
Alongside Mustafi, Gabriel was even more haphazard and appeared to have mislaid his understanding of the offside trap. Preston kept breaking through Arsenal's defensive lines and went closer still when Robinson escaped to the byline before his low pass was over-hit beyond an onrushing Hugill.
It was Arsenal who looked the lower-league outfit in those early stages as their attacking had hardly been much better than their defending. On the sidelines, cross-armed in his sleeping-bag coat, Arsene Wenger was distinctly unimpressed. His previous record against lower-division opposition in the FA Cup is almost unblemished.
Only Blackburn Rovers, a Championship club when winning 1-0 at the Emirates in 2013, had previously downed him, and he had never lost a third-round tie. But among the away fans, the odd cry of "Wenger out" could be heard. Eventually, understandably tired from their efforts, Preston slowed up as Arsenal gained a foothold for the last 15 minutes of the half without finding much in the way of fluency.
Whatever was said at half-time, where Wenger's habit is usually to say very little, paid instant dividends. From Alex Iwobi's neat layoff, Ramsey was given the type of space from which his shooting can be deadly, and within the first minute of the second period, Arsenal had managed to clean up the damage. They would have to wait to complete the job. Arsenal's aristocratic airs told as their manager's blushes were spared.