Shadow of Pep Guardiola is hanging over Pellegrini at Man City
There is some schadenfreude around Manchester City that after having lists of the 15 of their managers Sir Alex Ferguson outlasted quoted at them for all those years, it is Old Trafford that has the revolving door fitted now. Potentially five managers in three years will be extremely careless if Louis van Gaal's days really do prove to be numbered, some at the top of the club will say, behind thinly disguised smiles.
Well, their own door is hardly locked tight and non-revolving. The blue City suit Manuel Pellegrini wore last night looked tight and uncomfortable, and though you'll find none of the terrace resentment for him and his philosophies that Van Gaal is experiencing, the shadow of Pep Guardiola stalks him.
It's fairly remarkable that Pellegrini can actually find the magnanimity he does when the Catalan's name habitually surfaces in his press conference. His most recent: "I'm sure he'll manage Manchester City one day" was generosity in the extreme. But until that day, which does not seem so distant, the Chilean lurks in the lobby, awaiting the knock from the younger man.
Be careful what you wish for, Pellegrini may well tell Guardiola. City will bring riches and players and the Catalonian philosophy inculcated by his great friend Txiki Begiristain.
But in two catastrophic moments last night, we saw how City's director of football and his spending decisions offer no firm guarantees.
The £53m spent on Kevin de Bruyne looked ludicrous when, just past the half hour, he neither looked, nor blinked, nor saw David Silva when both were through on goal. He simply drove a shot wide.
More or less 10 seconds later, Theo Walcott demonstrated the fine margins at the top of the Premier League. He buried the ball Mesut Ozil had rolled into his path.
The second catastrophe came from £42m Eliaquim Mangala. He skewed a clearance at head height - a hospital pass to Fernandinho. It was a gift. The Arsenal side were able to recycle possession via Ozil into the path of Olivier Giroud, who rolled the ball home.
There were moments in a first-half which City took some control of when a different kind of vision might have flashed before Pellegrini. He was fielding Sergio Aguero and Silva together for only the sixth time this season, the other five having all delivered victories. But both players had gone by the 73rd minute.
To look at the players on whom Pellegrini still relies - Aguero, Silva, Yaya Toure and Joe Hart - was to be reminded once again that for all the money spent, the remnants of the Roberto Mancini era are the ones on whom he must by and large rely. It was Toure who clipped in the reply which created a brief hope.
By the end, Pellegrini was on his feet, searching for the evidence that there might be a game-changer in there for him; a moment of excellence from Raheem Sterling to steal something.
It was not to be.
Arsenal's belief is cemented that this could be the season which delivers for them.
Meantime, City and their manager look for evidence that they are in something better than a holding position, waiting for Guardiola over the course of five long months.