And with many fans starting to voice doubts about the Belgian’s commitment to the cause, the statistics will doubtless give boss Antonio Conte food for thought.
After all, he was then 23, with his colleague a decade older.
Jose Mourinho pleaded with Roman Abramovich not to let the deal go through — the Portuguese’s view based on football reasons far more than the £10million transfer fee.
But the Russian owner overruled his then manager, believing he owed Cech a debt after 11 years of superb service to the club.
Fourteen months later, it looks even more of a mistake than when John Terry said Cech would be worth “10-15 points a season” to Arsenal.
So far this season, Courtois — a £5m signing in 2011 — is, according to the number-crunchers, the WORST keeper in the Premier League.
Of the 23 glovemen who have played in the top flight, Courtois has the lowest save percentage.
He has faced 17 shots in six league games and nine – a staggering 53 per cent – have found the back of the Chelsea net.
Across the capital, bizarrely, Spurs have two of the top three, with second-choice Michel Vorm actually top of the pile with an 86 per cent success rate and their No 1 Hugo Lloris below only Manchester City’s Claudio Bravo.
Cech, the hero of Chelsea’s greatest hour — the 2012 Champions League win in Munich — is, perhaps surprisingly, only just above half-way in the keeper table, making 17 saves out of 24 on-target efforts against him.
Chelsea stopper Thibaut Courtois shows off his impressive basketball skills
But at The Emirates on Saturday night — as the hosts beat the Blues 3-0 — the Czech repelled everything that came at him.
Courtois, on the other hand, conceded three out of the five shots he faced.
The Belgian is not to blame for any of the nine goals that have gone past him in six Prem outings.
But he is simply not making the big, key saves he was expected to pull off — the ones he made time and again during his loan to Atletico.
And it is his enduring feelings for the country where he spent the first three years of hisChelsea career that are starting to colour views of him among the Stamford Bridge faithful.
In an interview with Madrid-based Marca, which infuriated many Chelsea supporters,Courtois revealed: “Real Madrid showed me a very nice gesture when I injured my knee last year. They sent me a fax to wish me a speedy recovery.”
Given that Courtois played for Real’s rivals Atletico, it appeared tantamount to tapping up the player.
And the Belgian added fuel to the fire as he added: “I have a contract with Chelsea for three more seasons.