Arsenal beat Manchester City 5-1 to keep their Premier League title hopes alive on Sunday, while Manchester United slumped to another meek 2-0 home defeat to Crystal Palace.
In the battle between the top two for the past two seasons, the Gunners prevailed to move within six points of leaders Liverpool, who have a game in hand.
"It is a great day for us, especially with the necessity that we had to win the game," said Arsenal boss Mikel Arteta.
Arsenal were gifted the perfect start inside two minutes as Manuel Akanji lost possession and Kai Havertz squared for Martin Odegaard to open the scoring.
Erling Haaland headed in his 250th career club goal early in the second half to bring City level.
But the defending champions are a pale shadow of their former selves this season and conceded within 105 seconds of the restart when Thomas Partey's shot deflected in off John Stones.
"It's happened all season, we are giving away too many things," said City manager Pep Guardiola.
"You cannot lose the control, it's 95 minutes. You cannot finish in the way we played."
Myles Lewis-Skelly would have been suspended if his controversial red card in a 1-0 win at Wolves last weekend had not been overturned.
The 18-year-old made the most of that reprieve by curling in Arsenal's third for his first goal for the club.
Havertz fired low and hard into the far corner with City cut open at will by the Arsenal counterattack on 76 minutes.
And another Arsenal teenager rounded off the rout when Ethan Nwaneri curled home in stoppage time.
Defeat leaves City still in fourth but now 15 points off the top and realistically dethroned after four consecutive seasons as champions.
Jean Philippe-Mateta was Palace's hero with both goals in the second half as United suffered a fifth defeat in their last six home league games.
Victory takes the Eagles above the Red Devils in the table as Oliver Glasner's side climb to 12th.
Three consecutive wins for United had lifted the mood around Old Trafford but it was back to square one for Ruben Amorim after another home display lacking in creativity and riddled with defensive lapses.
Kobbie Mainoo, who started as a makeshift center forward, hit the post with United's best effort of a bright opening before their attacking threat fizzled out.
Mateta opened the scoring on 64 minutes after Maxence Lacroix's header came back off the bar.
Worse was to follow for United as Lisandro Martinez had to be stretchered off with what appeared a serious knee injury.
"I think it's a serious situation," said Amorim. "Licha is really important for us, not just as a football player but the character he has, especially in this hard moment."
Palace showed no mercy to secure the three points when Daniel Munoz charged through the middle of the home side's defence and unselfishly squared for Mateta to knock in his sixth goal in five games.
Tottenham eased the pressure on under-fire manager Ange Postecoglou and fears they could be dragged into a relegation battle with a 2-0 win at Brentford.
The Bees were left to rue a number of missed chances against an injury-ravaged Tottenham defense.
Brentford also lent the visitors a helping hand with the opening goal as Vitaly Janelt headed Son Heung-min's corner into his own net on 29 minutes.
Yoane Wissa's header came off the bar as Brentford pushed for an equalizer.
But Spurs picked them off on the counterattack when Pape Sarr prodded through Valdimarsson's legs from Son's pass.
Victory lifts Tottenham to 14th and 10 points clear of the relegation zone.
