Arsenal overwhelmed Manchester United.
The Gunners ran out 3-0 winners, and the game was effectively over by the 20th minute.
Alexis Sanchez opened the scoring, before Mesut Ozil doubled Arsenal's lead and Sanchez completed the rout. Arsenal leapfrogged United into second position, and left Louis van Gaal's side facing what will feel like a long two-week wait for their next fixture.
Here's five things we learned from today's game.
Frustrating Arsenal
Only Arsenal could lose to Olympiakos in such a pathetic manner and then blitz a close rival a few days later. Arsene Wenger's side were unrecognisable from Tuesday defeat.
David Ospina received the majority of the blame for the Champions League defeat, but today's victory over Manchester United showed that there was a lot more at fault than a hapless goalkeeper.
Arsenal's attitude today was the polar opposite from that lame defeat. They were aggressive and combative, breaking with lightening pace and pressing United high up the pitch. Wenger's side didn't give United a moments rest on the ball and overwhelmed them in the opening 20 minutes.
Of course, a team isn't going to perform to such a high level in every game, but one would expect some consistency from a team with such quality.
However, that's never the case with Arsenal.
If Manchester City, United or even Chelsea produced such a convincing performance, then they'd be considered genuine title contenders, but not Arsenal.
You can be almost certain they won't win the league, and this performance was just a reminder of what the side is capable of, before inevitably coming undone as the season goes on.
It must be so frustrating to be a Gunners fan
Manchester United are made to pay for ponderous play
Arsenal play the same way in every game, and rarely change their tactics - an accusation that's been levelled at Arsene Wenger numerous times in recent years.
However, from the first whistle, Wenger's side ruthlessly exploited United's ponderous build-up play. They pressed and harried, forced United into mistakes and denied them the one thing Louis van Gaal craves more than anything - control.
The selection of both Michael Carrick and Bastian Schweinsteiger suggested that's exactly what Van Gaal sought from today's game, but it went disastrously wrong. While Schweinsteiger has performed well for United in games where they've been able to control possession, he badly struggled against Arsenal's high-tempo approach.
Both of United's central midfielders were made look their age, and simply couldn't deal with the speed of Arsenal's attacks. The absence of the more physical Morgan Schneiderlin was costly and difficult to fathom.
Arsenal's performance showed that possession football doesn't automatically equate to sterile possession, and it's Van Gaal, rather than Wenger, who was left looking tactically limited.
Manchester United's creaking defence
Everyone associated with Manchester United rejoiced when David de Gea's move to Real Madrid collapsed, and the 'keeper signed a new deal with the club.
In the seven games since the Spaniard returned, United have conceded nine goals. It'd be wrong to pin the blame entirely on De Gea for these goals - although he was arguably poor for Arsenal's opener today - and, despite the Spaniard's presence, United are still struggling at the back.
Matteo Darmian was substituted at half-time for the second consecutive game, and he was lucky to make it that far. The Italian full-back was awful. Darmian was about 30 yards out of position for Alexis Sanchez's second goal, and was given a torrid afternoon by the Chilean.
Ashley Young played as you would expect a winger to perform at full-back, while Chris Smalling, who has been excellent thus far this season, and Daley Blind also struggled. Blind has looked impressive stepping into midfield, and is a capable, technical footballer, but he is also vulnerable when up against physical players.
Bafetimbi Gomis gave him a rough time during Swansea's 2-1 victory, and Blind lot his physical duel with the pacey Walcott today.
During the opening month of the season, it looked as though United's defence would be their strongest asset this season. Not anymore.
Sanchez is back
After a World Cup, his first Premier League season, the Copa America and a shortened pre-season, Alexis Sanchez understandably started this season looking a but sluggish.
He's back now though.
The Chilean scored two wonderful goals. The first a clever, near-post back heel, the second a thunderous strike into the top corner that became a regular sight last season.
https://twitter.com/MiguelDelaney/status/650692639461875712
With Theo Walcott stretching the opposition defence, Mesut Ozil's passing ability and Santi Carzorla pulling the strings, the platform is there for Sanchez to have another brilliant season.
It might be time to bring the Chilean back into your Fantasy Football team.
What will it take for Wayne Rooney to lose his place?
Imagine another player put in the level of performances Wayne Rooney has this season. Imagine a striker not scoring or a deep lying forward not putting pressure on the opposition midfield when his team lose possession.
Imagine a player for a team with ambitions of winning the league possessing such a heavy touch, or incapable of sprinting past his marker.
How long do you think they'd remain in the team?
Players have been dropped and sold on the basis of performances like Wayne Rooney put in this season, but the United captain remains in the team.
Why? What does he bring to United? What signs has he offered that he's not in terminal decline?
It's difficult to justify Rooney's inclusion at this point, and only Van Gaal can say for certain why exactly he continues to persist with his faded star.
