Manchester City's title defence is imploding in a way Pep Guardiola has never experienced before.
Losing 2-1 to Manchester United left City with 32 points in the Premier League - Guardiola's lowest haul after 16 matches in 11 years in top-flight management.
Any fading prospect of a hat-trick of league titles looks to have been extinguished by City's fiercest foe in a game marred by United players being targeted with racist abuse and objects thrown by home fans.
The derby defeat left City 14 points behind Liverpool after the leaders won 3-0 at Bournemouth to nudge toward ending a 30-year championship drought.
"It is not realistic to think about catching up," Guardiola said.
Chelsea's grip on fourth place weakened with a 3-1 loss at Everton as Duncan Ferguson started his caretaker command with a signature success.
But the goal of the day came at Tottenham Hotspur where Son Heung-min ran almost the length of the field in a dazzling slalom effort to scored in a 5-0 victory over Burnley for Jose Mourinho's sixth-place team.
Chelsea's collapse helped Ole Gunnar Solskjaer cap a transformative week with United up to fifth place and only five points from the Champions League spots.
"There's more hard times for the doubters out there because we'll keep on working the way we're doing and we believe in what we're doing," Solskjaer said.
United tore apart City in the first half at the Etihad Stadium and Marcus Rashford put the visitors ahead from the penalty spot in the 23rd minute after being bundled over by Bernardo Silva.
The second goal inside six minutes was created by a slick exchange of passes between Daniel James and Anthony Martial, who applied the final touch past goalkeeper Ederson.
Although Nicolas Otamendi's header reduced the deficit in the 85th, City couldn't prevent United from claiming only a second away win of the season.
City's priority after the game was working with police to identity the fans who racially abused United duo Fred and Jesse Lingard and hurled objects at them as a corner was able to be taken during the second half.
"Thank God I have a lot of friends here in the locker room who hugged me, like Lingard," Fred told ESPN.
"I don't want to think about it. I just want to move on."
Liverpool's goals from Alex Oxlade-Chamberlain, Naby Keita and Mohamed Salah came in a devastating 19-minute spell either side of halftime to make it 33 league games unbeaten for Juergen Klopp's side stretching back into last season.
"The team performance was just really mature and professional," Klopp said.
"Just what we needed."
Son's mazy run before scoring Tottenham's third goal against Burnley reminded Mourinho of a goal scored by Brazil great Ronaldo for Barcelona.
"Even before this goal my son calls him 'Sonaldo,' and today he was Sonaldo Nazario," Mourinho said.
Harry Kane scored twice while Lucas Moura and Moussa Sissoko were also on target for Spurs.
Ferguson, a former Everton striker, already has the team out of the relegation zone after Marco Silva's firing with goals from Richarlison and Dominic Calvert-Lewin (two) sealing the points.
Newly-appointed Watford manager Nigel Pearson watched from the stands as the bottom-placed Hornets halted a three-game losing run by drawing 0-0 with eighth-placed Crystal Palace.
Australian Associated Press