Real Madrid’s title push faltered in the absence of injured top scorer Jude Bellingham as they surrendered a lead to draw 1-1 at struggling Rayo Vallecano.
Carlo Ancelotti’s men looked set to cruise to victory against their lowly city neighbours following a third-minute finish from Joselu.
But the LaLiga leaders missed the chance to move eight points clear after Raul de Tomas’ 27th-minute penalty earned Rayo a deserved derby point in their first match under new boss Inigo Perez.
Real’s advantage at the top could be cut to three points on Monday evening when nearest challengers Girona travel to fifth-placed Athletic Bilbao.
An underwhelming outing for the 14-time European champions was compounded in added time by the dismissal of substitute Dani Carvajal for two quickfire yellow cards.
Following a 1-0 Champions League win at RB Leipzig, Real were once again without 20-goal England star Bellingham due to an ankle issue as they made the short trip to out-of-form opposition who changed head coach in midweek.
Rayo appointed 36-year-old Perez on Wednesday after sacking Francisco Rodriguez the previous day on the back of just one win in 14 league games dating back to October.
The hosts endured a nightmare start to the new era as Real edged ahead inside three minutes thanks to a rapid counter-attack.
After visiting goalkeeper Andriy Lunin survived a nervy moment, Brahim Diaz released Federico Valverde down the right and his low cross was dispatched into the bottom right corner by a first-time finish from the unmarked Joselu.
Former Stoke and Newcastle forward Joselu, who was forced to wait for an incorrect offside call to be overturned for his opener to be awarded, had the ball in the net again in the 19th minute.
However, on this occasion, his close-range header was ruled out as the assistant referee was correct in adjudging the ball had gone out of play prior to Valverde crossing from the right.
Real at that stage appeared in complete control but Rayo took advantage of a VAR-awarded spot-kick to level.
Replays showed Oscar Trejo’s powerful effort was deflected over by the right fist of Eduardo Camavinga and former Real forward De Tomas confidently converted high down the centre of the goal to open his account for the season.
Real struggled to regain their rhythm, albeit the lively Valverde struck the outside of the left post with a long-range volley after Luka Modric’s corner was partially cleared.
Defensive dithering from Aurelien Tchouameni almost let in Alvaro Garcia immediately after the restart as Real’s unconvincing afternoon continued.
The away side enjoyed plenty of possession but lacked penetration as time ticked away.
Toni Kroos brought a superb save out of Rayo goalkeeper Stole Dimitrievski with a direct free-kick from distance, while fellow Real substitute Rodrygo had penalty appeals waved away after going to ground easily.
Spain full-back Carvajal, who came on in the 75th minute, then departed prematurely after petulantly lashing out at Kike Perez.
And the lacklustre visitors could have few complaints about dropping points for only the sixth time this season as Rayo marked the start of Perez’s reign with a surprise result.