Carlos Carvalhal's second victory in charge of the Swans was further evidence of the manager bounce effect, as was Paul Lambert's 2-0 win for Stoke City against Huddersfield Town. Together, these two results made the relegation battle tighter than ever; there is now just six points between 20th and 10th.
Here are three things we learnt from the weekend action:
1) Arsenal's reversion to a back four solidifies midfield
Arsene Wenger doesn't like changing formation, but for the first time in the league this season he reverted to the 4-2-3-1 system that has defined the vast majority of his 22 year career in north London. The result was a considerably more resilient central midfield and simpler roles for Alex Iwobi and Alexandre Lacazette, both of whom have struggled for form this season.
Nacho Monreal, who scored a goal and assisted two more, also seemed to benefit from a less complex role in the side. He frequently overlapped Iwobi from the left to good effect, allowing the Nigerian to find space when drifting inside. But the biggest reason for Arsenal's success was their control of central midfield, with Mohamed Elneny at the base allowing Jack Wilshere to roam forward without pressure.
2) Batshuayi & Willian show why Conte should never have abandoned his 3-4-2-1
Chelsea also changed their formation for the 2017/18 season and, like their London rivals, benefitted at the weekend from switching back to something more familiar. Antonio Conte's team have consistently used a flat 3-5-1-1 or 3-5-2 this season, which heaps pressure onto Eden Hazard as the sole playmaker in the side.
But the Belgian was finally freed against Brighton thanks to the addition of Willian (to make a 3-4-2-1 like last season) and the excellent link-up play of Michy Batshuayi. The Belgian striker dropped off the front line to distract the opposition midfield, which in turn created space for Hazard and Willian to drive forward.
It is about time Conte reverted to the formation he has bizarrely abandoned this year - and give Batshuayi the chance he clearly deserves.
3) Stand-off Swans defence highlights Carvalhal's main strengths
Swansea City ran out deserved 1-0 winners in Wales on Monday evening thanks to a typical Carlos Carvalhal performance; it looks as though the Swans have already been absorbing the Portuguese's tactical methods.
The most striking feature was the resilience of their narrow defensive shell. Swansea stood right off Liverpool to the extent that the visitors' centre-backs freely held possession just 35 yards from goal, which explains why Virgil van Dijk provided the two best through balls of the match. This tactic hugely limited space in the final third, stunting Liverpool's narrow attacking lines.
Equally impressive was the calm way in which Swansea passed their way out of trouble and made excellent decisions when breaking. This was another hallmark of Carvalhal's Sheffield Wednesday.
Best of the week – Paul Lambert's fast start
The former Aston Villa manager has spent a lot of time with top-level managers during his time off as he attempts to learn more about the game. This might explain why his Stoke City side did not attempt patient possession football against Huddersfield Town; Paul Lambert has moved on.
Joe Allen and Charlie Adam were Stoke's best players but this was a team performance. Stoke completed more sprints than in any other game this season, suggesting Lambert's biggest impact has been to refocus and re-energise this side. From a tactical perspective, it was interesting to see Eric Maxim Choupo-Moting, Xherdan Shaqiri, and Mame Biram Diouf frequently swap positions as the front three.
Worst of the week - Liverpool's tactical timidity
Swansea deserved their win for a resolute defensive performance, but there job was made pretty easy by an appalling Liverpool performance just eight days after that magnificent 4-3 victory against Manchester City. We know Liverpool are better when afforded space to attack into by bigger teams, but by now they really should have worked out how to overcome deep-lying opposition.
Not a single Liverpool playmaker had the thoughtfulness to drop deeper than the Swans' midfield line and attempt to clip balls into the box (something Philippe Coutinho would have done). They also didn't peel out wide to try and stretch the defensive shell, or even move quickly enough from within the centre of the bodies to create quick-tempo one-twos. If you don't move, then you won't break down that sort of defence.