Manchester City suffered their first Premier League loss since December as Bournemouth stunned the champions, while Arsenal were rocked by Newcastle and Liverpool seized top spot on Saturday.
City were unbeaten in their previous 32 league games dating back to a defeat at Aston Villa last year.
But Pep Guardiola's second-placed side saw that streak come to an unexpected end in a 2-1 loss on England's south coast.
The Cherries had never beaten City in their 21 previous meetings, losing 19 of those matches, yet Andoni Iraola's team sprang a huge upset to derail the champions' push for a fifth successive title.
Bournemouth recently damaged Arsenal's title hopes with a 2-0 win at the Vitality Stadium and they inflicted pain on City as well.
Guardiola had claimed City faced an injury "emergency" after they suffered fitness problems in Wednesday's League Cup defeat at Tottenham.
But Manuel Akanji, Kyle Walker and Josko Gvardiol all started against Bournemouth after injury doubts, with Kevin De Bruyne, Savinho and Jeremy Doku fit enough to be named among the substitutes.
Exhausted or not, City were rocked in the ninth minute when Bournemouth winger Antoine Semenyo drilled Milos Kerkez's cross past Ederson from inside the area.
Guardiola's men were unable to muster a response to that blow and Evanilson doubled Bournemouth's lead in the 64th minute with a composed finish from Kerkez's cross.
Gvardiol's header reduced the deficit in the 82nd minute, but it was too late to save City from a second defeat in four days.
NEWCASTLE DEFEAT ARSENAL
Newcastle put a huge dent in fourth-placed Arsenal's title aspirations with a 1-0 win at St James' Park.
Alexander Isak netted in the 12th minute, heading home Anthony Gordon's pinpoint cross.
Injury-hit Arsenal struggled to get out of first gear and produced just one shot on target in the entire game.
Mikel Arteta's team, runners-up to City for the past two years, have taken just one point from their last three games as their push for a first title since 2004 was derailed by a second league defeat this term.
"Today we weren't our best version. It's about how you react to that. We're not going to find the right words or answers to describe how we feel," said Arteta, whose side are seven points adrift of first place.
LIVERPOOL'S LATE POWER SURGE
At Anfield, Liverpool were in danger of a surprise loss of their own before regrouping to take advantage of their rivals' stumbles with a 2-1 win over Brighton.
Ferdi Kadioglu gave Brighton the lead in the 14th minute with a fierce strike that cannoned in off the post after Danny Welbeck flicked on Kaoru Mitoma's cross.
But Liverpool had beaten Brighton in the League Cup last 16 in midweek and they repeated the trick thanks to a late revival.
Cody Gakpo bagged the equaliser in the 70th minute with a cross that looped straight into the net.
Two minutes later, Mohamed Salah put Liverpool ahead, the Egypt forward curling a fine finish into the top corner for his ninth goal this season.
In Arne Slot's first season in charge, Liverpool are two points clear of City after their eighth win in 10 league games.
FOREST'S MOMENTUM BUILDS
Nottingham Forest are up to third place after beating 10-man West Ham 3-0 to make it three consecutive top-flight victories for the first time since 1999.
Chris Wood grabbed his eighth goal in 10 league games as the New Zealand striker headed home after 27 minutes.
West Ham had Edson Alvarez sent off in first-half stoppage time for two bookings.
Callum Hudson-Odoi struck in the 65th minute and Ola Aina sealed the points 12 minutes from fulltime at the City Ground.
Jordan Ayew's stoppage-time equaliser denied Ipswich their first top-flight win since 2002 as Leicester rescued a 1-1 draw at Portman Road.
Leif Davis's 55th-minute volley put Ipswich ahead but the hosts had Kalvin Phillips sent off in the 77th minute.
Ayew levelled with seconds left to leave third-bottom Ipswich winless after 10 games.
Second-bottom Southampton earned their first league win this season as Adam Armstrong's 85th-minute strike sealed a 1-0 success against Everton.