La Liga leaders Barcelona slumped to a shock first loss of the season after suffering a 2-1 defeat at struggling Leganes after conceding twice in two second-half minutes.
Coach Ernesto Valverde's squad rotation backfired as the unfancied hosts held on to record their first top-flight win over Barcelona.
Philippe Coutinho gave the champions the lead in the 12th minute with a classy volley and Lionel Messi smacked a shot against the bar as Barca, resting Jordi Alba and Luis Suarez, made a strong start against Leganes, who began the game bottom of the table.
Barca's comfortable hold on the game dramatically fell apart shortly after the interval when Nabil El Zhar headed home a looping cross in the 52nd minute and 20-year-old Oscar Rodriguez turned in a second goal barely sixty seconds later to the joy of the 12,000 fans crammed into the Butarque stadium.
Real Madrid failed to capitalise on Barca's shock defeat after being humbled by Sevilla at the Ramon Sanchez Pizjuan.
Their rivals' defeat gave Real an opportunity to go top of LaLiga but Sevilla were in no mood to be obliging hosts as they ran out 3-0 winners, scoring three times in an incredible opening half.
Andre Silva bagged a brace and the in-form Wissam Ben Yedder also got on the scoresheet while Real saw Luka Modric's second-half effort disallowed after consultation with the video assistant referee.
It was a first defeat of the season for Real at a ground where they have lost on their last four visits in the league.
Elsewhere, Valencia are still searching for their first win of the season after Iago Aspas struck eight minutes from time to rescue a 1-1 draw for Celta Vigo.
Michy Batshuayi grabbed his first goal for Valencia in the 25th minute but Los Che settled for their fourth stalemate in five games following Aspas' late leveller.
Finally, Villarreal scored three times in the last 25 minutes in a 3-0 win at Athletic Bilbao.
Pablo Fornals struck after the hour mark while Ramiro Funes Mori doubled the Yellow Submarine's lead with 10 minute remaining.
Substitute Karl Toko Ekambi added gloss to the scoreline in the 89th minute.