Every manager who has ever feuded with Jose Mourinho knows that the time to worry is once he starts making peace with expansive public gestures of friendship, and talking with a laboured sincerity about a mutual responsibility to the game to be respectful.
The bad news for Antonio Conte is that he has already reached this point with Mourinho, his status as chief enemy revoked, his threat level radically downgraded.
This was a strange game, after which even Mourinho admitted that Chelsea had dominated the opening 45 minutes.
By the end of it, the problems of the last few weeks looked significantly worse for Conte and the United manager knew that he has more dangerous rivals than the current champions.
After an afternoon of handshake conventions fulfilled, Mourinho adopted his well-practised rueful peacemaker aspect to announce the end of bad vibes between him and Conte.
Mourinho’s players had done well in the second half, most notably the two Chelsea old boys, Romelu Lukaku and Nemanja Matic.
Lukaku scored the first and created the second for Jesse Lingard, while Matic shut the back door on Chelsea and, even when Conte unleashed his full firepower on United, it barely made a difference.
It was hard to say how Chelsea lost from having a first-half lead given to them by Willian, showing some of the sparkling form of last Tuesday’s draw with Barcelona and well assisted by Eden Hazard.
Scott McTominay will always remember the day he had to man-mark one of the English game’s finest talents.
By and large the young midfielder did a good job. By 75 minutes, Conte judged his No 10 to be exhausted and replaced him with Pedro.
Mourinho said later that it was the technical aspects of his team’s first-half performance that meant they started slowly, some high-level detail about the pressing distances and the shape of his “midfield square”.
“We can be speaking about tactics and positions and football science but I think to win against the big teams – and it happens when other teams like Newcastle beat us – the attitude has to be really special, and the players showed that,” Mourinho said afterwards.
Lukaku’s mastery of the ball is often imperfect, but he hung in there and scored a good equaliser before half-time and then clipped in a cross for the substitute Lingard to head in at the near post.
There was a first-half moment before the goal when Old Trafford sighed at the ease with which Antonio Rudiger dispossessed the United striker, and yet he turned it around.
The next time United are back at Old Trafford, the visitors will be Liverpool, against whom they conceded the initiative of their early-season promise when they played so defensively in the draw at Anfield in October.
That will be an even more serious test than Chelsea, who have now lost three of their last four league games and find themselves in fifth and in serious danger, as Conte admitted, of missing out on the Champions League places.
The Chelsea manager had begun the game shaking hands with Mourinho, and there was a moment during the match when the latter seemed to successfully break the chill with a joke.
Conte kept the celebrations for Willian’s goal at the lower end of the scale by his standards, although at that point he may have felt he was going to see something different from his team.
“You have to manage the game better and with experience, with maturity, get three points,” he said later.
“Instead for another time we are talking about a loss and we must be very disappointed.”
There was one grievance over an offside decision against Alvaro Morata in the 85th minute when he put the ball in United’s goal from a pass by substitute Cesc Fabregas, for which Conte again demanded the swift introduction of video assistant referees.
This one was hard to judge, with many of the United players seeming to have stopped at the first sign of the flag being raised.
Chelsea had counter-attacked beautifully for the goal, Willian winning a header in his own area and bringing the ball clear.
He passed it into Hazard and continued his run, anticipating the excellent return pass from his team-mate, who doubled back before releasing.
The Brazilian beat David De Gea at his near post, a shot that you could say the United goalkeeper should have dealt with better.
The equaliser arrived seven minutes later when Lukaku, with his back to goal, laid the ball off to Matic.
From there, it went to Alexis Sanchez and on to Anthony Martial, who played a short ball into the path of Lukaku as he ran through a crowded area. On this occasion, his touch did not let him down: there was one with the left foot to control it and the right foot to bury it.
In the second half, Lukaku had already forced an excellent save from Thibaut Courtois with a flying volley from Sanchez’s cross when he delivered a near-post cross for Lingard, who had gone on in place of Martial, to head it in.
Conte ended the game with Olivier Giroud and Morata in attack and Fabregas on for Danny Drinkwater, but nothing worked and all that was left for him was another defeat, and Mourinho’s condolences, which must have been a very bitter pill indeed.