The victory of Manchester United over Manchester City utterly aggravated the fight for medals in the Premier League.
If Arsenal continues to lead confidently, then the townspeople, who previously seemed inaccessible, allowed their principled rival to practically catch up with themselves in the table.
And now Eric ten Hag's wards may well challenge the Londoners in the fight for gold, if they manage to beat them in the next round.
The progress of the Mancunians is truly admirable, because after a pause for the World Cup, they literally changed.
The team has already won six victories in a row in all competitions.
In the Premier League, a successful series in total includes five matches.
In the FA Cup, Everton managed to get through, and in the quarter-finals of the League Cup - Charlton.
Even Arsenal's performance in this segment is more modest: two wins and one draw in the national championship.
The main thing is that the wards finally accepted Erik ten Hag and his ideas and began to put them into practice.
They are already second in the Premier League in terms of ball possession and pass percentage, just behind City (57.6% and 85.5% respectively).
In pressing, the team is also one of the best, demonstrating excellent physical readiness and not allowing opponents to quickly launch attacks.
At the same time, the Dutchman himself is always ready to present unpleasant surprises to his counterparts.
In the derby, this manifested itself especially clearly.
The specialist unexpectedly relied on the 4-2-3-1 formation and released two destroyer defensive midfielders at once - Casemiro and Fred.
With this, he put Josep Guardiola in a dead end.
The Brazilians had a great meeting and practically did not allow the guests to attack through the center, especially in the first half.
Fred, who got a chance, became one of the best on the field in terms of defensive actions, having made three tackles and one interception.
As a result, the opponents simply did not understand what to do with the ball before the break, although they had almost 70% of it.
As already mentioned, the support zone was tightly closed and it turned out to be unrealistic to penetrate through it to someone else's penalty area.
The hosts met opponents in the middle block so well that they did not allow them to move into the final third of the field.
The townspeople regularly had to fall on the flanks, from where it was extremely difficult to create a danger.
As a result, the first shot on target by David De Gea was delivered only in the 60th minute, but it immediately turned out to be effective.
Ten Hag also reacted exemplarily to the failure.
He removed a tired Christian Eriksen from the field and, switching to a three-forward scheme, threw a fresh young Alejandro Garnacho into the battle on the left flank of the attack.
This instantly paid off.
In the 78th minute, Bruno Fernandes equalized the score, although the ball turned out to be controversial.
Marcus Rashford, who was offside, covered the Portuguese with his back from the defender, but the judges, after a little thought, pointed to the center.
And literally in the next counterattack, the same Rashford put an end to it just from the transfer of Garnacho.
The Argentinean had a great ball on the left flank and, having swung Nathan Ake, gave an assist to a partner.
The effectiveness of the Englishman is a special topic.
Last season, he scored only five times in all tournaments, but with the advent of ten Haga, he blossomed.
The forward has already hit the opponents' gates in total three times more - 15 and added six assists to them.
At the same time, he not only realizes his chances great, but also does a huge amount of work in pressing.
It is up to Marcus to prevent the defender from making the first pass at the start of the attack.
For example, in the derby, when taking out from other people's gates, he regularly shifted to the counterpart closest to Ederson, interfering with the draw.
The attacker's attitude is also admirable.
Significant moment: at the end of the first half, he, trying to get the ball on the edge, pulled a muscle.
It seemed that Rashford was not able to continue the match, because he was assisted for a couple of minutes.
But he returned to the field, and in the end he took a direct part in both goals.
Along the way, the player became the first Manchester United player since Cristiano Ronaldo to score in seven consecutive matches for the club.
The magnificent game of the Englishman allowed the fans to quickly forget about the Portuguese.
It is no coincidence that the team's successful streak coincided with his departure.
He no longer brought benefits, but, regularly remaining on the bench, significantly spoiled the atmosphere in the locker room.
The results showed that ten Hag was right to go into conflict with the star ward.
Obviously, he was not ready to work out in pressure like Rashford, which is necessary in the Dutchman's scheme, but he could no longer score on the same scale.
But the purchase of Casemiro had an ideal effect on the Mankuanians.
Many raised questions about his acquisition, but the Brazilian confirmed his importance for the team with his actions.
Without it, the support zone is now impossible to imagine.
The rookie is Manchester United's best in tackling average in Premier League games (3.1) and in the top 6 in steals (1.1).
Moreover, he does not get hung up on destruction, but also perfectly starts attacks from the depths.
What, for example, is his magnificent throw at Rashford in the first half of the meeting with City, when the partner beat Ederson, who jumped out of the gate, but failed to break through Manuel Akanji, who took his place on the line.
The order in the support zone led to the fact that Manchester United finally got the game on the defensive.
Last season, Manchester missed a lot, but after the end of the World Cup, they allowed their opponents to score only twice.
De Gea also comes into play much less often.
As already mentioned, in the derby, the guests struck the first shot on target only after an hour had passed.
But the affairs of Manchester City, on the contrary, are not developing in the best way, and the next defeat clearly confirmed this.
In the fall, the impression was created that the townspeople had no equal and they were obliged to defend the title.
However, in December-January, Josep Guardiola's wards first parted ways with Everton, and now lost to Manchester United.
Along the way, they flew out of the League Cup, losing sensationally to outsiders Southampton.
Moreover, the current champion lost the victory twice.
In the confrontation with Everton, he also opened the scoring thanks to an accurate strike from Erling Haaland, but after the break he allowed Demarai Gray to score.
The team can no longer always keep the result that suits it, which indicates not the best physical shape.
Haaland himself, who scored on an industrial scale in the first part of the season, does not look so powerful either.
In three matches of the new year, he has not scored even once.
The meeting with Manchester United turned out to be a failure for the Norwegian.
It was securely closed by Raphael Varane and Luke Shaw and hardly met the ball.
In the first half, the striker made only eight touches and as a result failed to deliver a single blow.
It seems that defenders playing in the Premier League have gradually adapted to the striker's style of play and learned to neutralize him.