Napoleon as we know asked a single question when it came to promoting one of his generals to the rank of marshal: “Is he lucky?” After Arsenal’s astonishing victory over favourites Chelsea in the FA Cup Final, the question might be asked of Arsene Wenger and answered strongly in the affirmative.

When the suspension of his key centre-back Laurent Koscielny, guilty of a mindlessly silly red card foul, together with the loss, injured, of a reckless Gabriel Paulista deprived the Gunners of two key defenders, there was nothing to do but recall in desperation the big German centre-back, Per Mertesacker.

So severe had been his last season’s injury that he had played no more than a fraction of Arsenal’s last League game against Everton, before the Cup Final. How could he be expected to withstand the rapier thrust of such as Eden Hazard, Diego Costa and Pedro? The answer was, resiliently and defiantly.

Wenger had deployed him in desperation because there was literally nobody else. Neither he nor any fan has the right to expect what we saw from Mertesacker, a dominant display in which he commanded the middle of defence, not only in the air, but even on the ground where it might have been expected the likes of Costa in particular would be too quick and elusive for him.

Where indeed were the Chelsea stars, who has inspired the team to its triumph in the Premiership? N’Golo Kante, footballer of the season twice over, was at Wembley a negligible figure. Hazard, who had been in such dazzling form in attack, was comfortably contained by the Arsenal defence. No one in the Chelsea team could match the irresistable Alexis Sanchez. Yes, there were serious doubts about Arsenal’s stunning, early opening goal. Sanchez seemed certainly to handle to get the ball under control. Aaron Ramsey was emphatically standing in an offside position, though it was determined that he was not interfering with the play. Which reminds one of Bill Shankly’s observation on the subject: “If he’s not interfering with the play, what is he doing on the field?”

In fact Chelsea’s goalkeeper, Thibaut Courtois, insisted that he had been distracted by Ramsey. “If he is not standing there, I might have got to the ball.” He was equally irate about Sanchez’s handball but added, “We must be honest. Arsenal were just better.”

But goals change the psychology of games, and Sanchez’s goal gave Arsenal a tremendous impulse, while plainly shaking Chelsea’s self-belief. Players who had been inconsistent, sometimes inadequate, such as the German attacker Ozil and the the Swiss international Xhaka, excelled. Quite outshing even Hazard.

So, three days later, Wenger was able to meet the Arsenal boad with a strong claim to have his managerial contract renewed. Before the Final, his claims to stay seemed somewhat fragile. Fifth place in the Premiership was a fearful blow, excluding the Gunners from the Champions Cup. Now he has been controversially retained. Sanchez will probably go. The outlook is hardly promising.