Arsenal and Manchester United have fallen a long way since the heyday of their Premier League rivalry, a fact clearly emphasised by the contrast between the 90s montages in the Sky Sports coverage and the dreadful quality in the game itself.

Both teams lack leaders and both lack a clear direction at the moment.

Things are improving for Tottenham Hotpsur and Leicester City, who both recorded important wins at the weekend and will have been heartened to see two of their rivals for a top-four finish drop points on Monday night.

Here are three things we learnt from the weekend action:

1) Klopp's switch to 4-2-4 does enough to get past stubborn Sheffield United

Sheffield United were unlucky not to get a point at Anfield. They were extremely well organised in sitting off and squeezing out space through the middle, their front five forming a ring around Fabinho that meant the centre-backs – left alone in possession – only had the option of passing into the flanks. United's use of wing-backs meant they could step out to meet the Liverpool full-backs, leading to a fractured game for the hosts in which the front three were stumped.

Liverpool didn't help themselves by using an oddly shaped midfield. Georginio Wijnaldum sat directly in front of the overcrowded Fabinho for most of the match and Jordan Henderson ran up and down the right wing to no great effect. He should have been more central to build through the middle.

However, that changed when Jurgen Klopp brought Divock Origi onto the pitch in place of Henderson and switched to a gung-ho 4-2-4 formation. Roberto Firmino played just behind Mohamed Salah with Origi and Sadio Mane moving very wide to receive longer passes into the channels. It created a wild and open contest, but ultimately it proved to be the right decision as Origi played a big hand in the winner.

2) Ndombele finds his feet in crucial opening half hour for Spurs

Southampton dominated possession after Serge Aurier's red card as Spurs had to sit back and dig deep for the three points, but from a tactical perspective the most interesting portion of the match was the opening half hour. Tottenham began in a diamond 4-4-2 that layered onto Southampton's 3-4-3 in such a way that Tanguy Ndombele had lots of space between right wing-back James Ward-Prowse and midfielder Oriol Romeu.

Ndombele was excellent, considerably raising the tempo compared to recent sluggish Spurs performances against bottom-half clubs. He is able to wriggle out of danger and use his strength to dribble past people, opening up the pitch and injecting energy into those around him. Ward-Prowse was too busy trying to get a handle on Son Heung-Min (who hugged the left touchline) to help Romeu, which is why Ndombele increasingly turned the screw until scoring the opener.

Southampton improved in the second half by switching to a 4-3-3 that felt more balanced against Ndombele, but the damage had already been done. Tottenham's new signing looks set to transform their season.

3) Ceballos introduction shows Emery was overly cautious at Old Trafford

Nobody was surprised by the dreadful quality of the 1-1 draw at Old Trafford on Monday night. However, Arsenal fans will probably be the more frustrated after manager Unai Emery fielded a surprisingly defensive team, deploying three holding midfielders – Granit Xhaka, Lucas Torreira, and Matteo Guendouzi – despite Manchester United looking vulnerable this season.

Leicester City made a similar mistake recently and also dropped points, suggesting some managers are yet to realise the extent of United's crisis; they are there for the taking, so long as a bold attacking approach is taken. Xhaka was predictably very poor and Torreira also went missing for long periods, further emphasising the mistake of playing both against a midfield that just wasn't up to the challenge. Paul Pogba looked disinterested and Jesse Lingard was once again anonymous.

Things improved for Arsenal when Dani Ceballas was introduced. He added an elegance in possession and quickness of thought that saw the Gunners build into the United half more consistently, opening up the match for a more entertaining final half an hour. Perhaps Emery was happy with a point, but he shouldn't be. If playing from the start, Ceballos's forward-thinking approach could have won this game for the visitors.

Best of the week – Cahill's influence at Crystal Palace

Palace have already amassed 11 points this season, which means they can slip into pretty poor relegation form for the rest of the campaign and probably still stay up with 36-38 points. Having kept their third clean sheet of the season on Saturday in a 2-0 win over Norwich City, it is time more attention is given to the shrewd acquisition of Gary Cahill over the summer.

Cahill has made more clearances (5.5 per game) and more blocks (1.2 per game) than any other Palace player, putting his body on the line when it matters and leading a rigidly organised back line. He was impressive again at the weekend, this time adding a composure in possession that has been missing at Palace in recent years.

Worst of the Week – Newcastle's back four

Steve Bruce almost exclusively uses a back five these days, which perhaps explains why Newcastle United were so clueless in a 5-0 defeat to Leicester City on Saturday. The way their full-backs defended suggests they had not been coached how to function in a back four.

Four of the Foxes' goal came via beating a Newcastle full-back who got too tight to the player, presumably because they were used to being free to close down with a third centre-back covering behind them. That isn't the case in a four, and it showed: Paul Dummett was turned ahead of the opener, Emil Krafth was completely out of position for the second, and Dummett lost his marker for the third.

Newcastle's full-backs were reckless in charging out of the back line, suggesting Bruce had not adequately re-coached his players for the formation change deployed at Leicester.