At kick-off, the torrential rain lashing down at Old Trafford felt like the foreboding of something significant; something potentially era-defining for one of these two managers.
That might be the case, such was the potency of a 2-1 victory for Ruben Amorim in a game that contained so many of the hallmarks of a swashbuckling and talented Manchester United at their best.
But as the chaos unfolded, as the red cards and the goals and the substitutions piled up, it wasn’t long before that brooding sensation gave way.
Because, as the players splashed about, sometimes struggling to kick the ball far forward on the sodden surface, the rain came to feel like a symbol of the chaos that was this wildly fun and frenzied 90 minutes in Manchester.
On the one hand there was too much going on here to sift through and present a coherent story; this was the first match in Premier League history to see at least two goals, two red cards and two substitutions in the first half.
On the other, the game was effectively won in an opening half in which Chelsea goalkeeper Robert Sanchez saw red and Man Utd scored both their goals – courtesy of a tactical change from Enzo Maresca that he probably regretted.
Maresca's tactical change plays to United's strengths
Not for the first time this season United raced out of the blocks, and credit to Amorim for continuing the pattern of fast and direct starts despite the club’s mixed results.
It was an early long ball forward and flick-on from Benjamin Sesko – the kind of route-one approach that has meant United peppered the goal with shots in the opening passages of games this season – that led to Sanchez’s early red card.
That was always going to have a big impact on the game. But it’s on Maresca that it was quite so big.
Critics of the Chelsea head coach have suggested he is conservative in his instincts, playing a slow possession game more concerned with control than attacking football, and perhaps that explains his immediate shift to a 5-3-1 formation.
Withdrawing wingers Pedro Neto and Estevao Willian to replace the goalkeeper and move to a back five, Chelsea now had no speed on the wings to launch counter-attacks, isolating Joao Pedro alone in front of a flat midfield three.
More importantly, the head coach perhaps sent his players a fearful message. They duly shrank, playing on the edge of their own box and inviting pressure, helping a Man Utd team schooled in a 3-4-3 formation that was formulated at Sporting, where a simple attack-versus-defence was the default pattern.
Amorim, in other words, was – for arguably the first time in England – in his element.
Sitting deep, Chelsea conceded two goals that resulted from having too many bodies cluttering the area. Had they aggressively stuck to the game plan, perhaps in a 4-4-1, they may have hurt United more.
Instead Man Utd could dominate the territory, focusing solely on their own attacking patterns.
Man Utd play with newfound urgency
It’s easier against 10 men, but Man Utd were fluent and urgent in their approach for the first half especially, pressing home the advantage with the direct running of Amad, Bryan Mbeumo, and Sesko in particular.
Throughout the game we saw Matthijs de Ligt and Luke Shaw push up to hold the ball in advanced midfield positions, reflecting a part of Amorim’s tactical strategy we have rarely seen.
The problems with a two-man midfield are supposed to be offset by the aggressive stepping up of the outside centre-backs. A few more onlookers will have been converted today.
De Ligt's touch map v Chelsea
The better parts of United’s game began to diminish in the second half after Casemiro’s red card, and particularly in the final 20 minutes, after Maresca had finally moved to a slightly odd 4-3-2 and both teams – in completely unfamiliar formations, fighting biblical weather – descended into carnage.
To get a sense of how disorganised Chelsea were in their approach, and how often they changed things up in the second half, take a look at their average positions below.
Chelsea's average positions v Man Utd
However, even here Man Utd looked the better team, largely because Chelsea struggled for numbers in attack. Without the injured Cole Palmer, and without pace to run in behind (Maresca may regret leaving Alejandro Garnacho on the bench), Chelsea arguably did not push hard enough.
They did eventually score, through Trevoh Chalobah’s brilliant header, but his goal proved to be a consolation only. On the balance of play Chelsea can’t really complain.
Sometimes football is tactical, sometimes it’s about riding the rhythms that nobody can control, be they rain or red cards.
Today, it was both. And Man Utd were deserved winners.