The Czech stopper had lost his place as number one to Thibaut Courtois, but the decision to let him join a direct title rival was considered a huge risk.
The Blues were expected to challenge for the title along with the Gunners, but their start to the season could not have been more of a disaster.
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And stats released by the Premier League prove just how big an influence Cech has had at Arsenal since his arrival while Chelsea struggle for any sort of consistency.
The Czech 'keeper has continued the form that made him one of the world's most revered stoppers during his 11-year spell at Stamford Bridge.
Making 31 saves, the fourth most this season, and holding the best save percentage in the top flight, an outstanding 81.58 percent.
To top it off, he has already kept four clean sheets for the Gunners. Only Joe Hart - on five - has more.
Chelsea sit 16th in the table following their worst start to a season in 37 years and the injury to Courtois has compounded their misery.
Now, we are by no means saying the Blues should have kept hold of Cech, as he was always likely to leave after spending the majority of last season on the bench.
However, his arrival at Arsenal has inspired the Gunners, who have climbed up to second in the table following a shaky start.
It is still early days and fortunes can change, but the decision to allow the 33-year-old to join Arsenal is proving to be a huge error of judgment by the Chelsea hierarchy.
Should Chelsea have insisted Petr Cech moved away from the Premier League? Have your say in the comments section below!
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