Quickfire Sevilla upset Real Madrid
Mali international Keita put Sevilla ahead when he sent an unstoppable long-distance shot fizzing into the back of the net on 19 minutes and Luis Fabiano made it 2-0 before Real had a chance to respond when he smashed home a rebound.
Real were reduced to 10 men early in the second half when former Sevilla defender Sergio Ramos was sent off after picking up a second booking for a foul on Diego Capel.
Real stayed top of the table despite their second defeat of the season but arch-rivals Barcelona will cut their lead to a point if they beat struggling Real Betis on Sunday.
Sevilla remained in 10th place on 15 points but have a game in hand.
Valencia moved up to fourth place in the standings, level on 21 points with Barcelona and Villarreal after a neatly taken double from striker Fernando Morientes earned them a 2-0 win at Real Mallorca.
The islanders looked the more dangerous side for most of the match but Morientes made the most of two isolated chances to give his side a win that eased the tension after heavy defeats by Sevilla and Real Madrid.
The action at the Sanchez Pizjuan got off to a breathless start as the two sides gave no quarter in the midfield and looked to attack at every opportunity.
It was Sevilla, though, who looked the sharper of the two sides as they tested the Real defence with a series of high-speed attacks and took the lead with a stunning strike from Keita on 19 minutes.
Casillas had no chance as the former Lens midfielder let fly from 25 metres after the ball fell to him following a poor clearance.
Real were still dusting themselves down when Sevilla hit them again, Brazilian striker Luis Fabiano scoring his seventh goal of the season when he fired in after Casillas had blocked a stinging shot from Frederic Kanoute.
Sevilla were unlucky not to be awarded a penalty four minutes later when speedy winger Jesus Navas was brought down by Mahamadou Diarra in the area but the referee waved play on.
Real suffered another setback with the Ramos sending-off, but Sevilla were unable to extend their lead despite their numerical advantage.
Luis Fabiano blazed over the bar after beating the offside trap two minutes after the dismissal and Capel missed the target in the closing stages following a fine run into the area.