Casillas saw red for Real after just two minutes but his
team-mates managed to hold on wioth ten men.
Real Madrid played for 89 minutes with just 10 men to beat Espanyol 1-0 at the Cornella-El Prat Stadium in Barcelona.
Real Madrid saw goalkeeper Iker Casillas sent off in the first minute for a professional foul on Espanyol striker Jose Callejon, but his side held on with few problems despite having a player less and won the game thanks to a goal from Marcelo midway through the first period.
Meanwhile Barcelona's 16-game winning run came to an end with a 1-1 draw away to Sporting Gijon on Saturday night.
David Barral put Sporting ahead after 15 minutes to send the fans in a packed El Molinon stadium wild. Sporting then withstood wave after wave of Barcelona attacks before David Villa scored the equalizer with just 10 minutes remaining.
The fact that Barcelona dropped two points means Real Madrid reduced their lead at the top of the table to five points.
Elsewhere the weekend saw Villarreal suffer a second consecutive setback as they lost 1-0 in La Coruna with Alberto Lopo's second half strike giving Deportivo three vital points, which lifted them out of the drop zone.
The struggle against relegation got a lot tighter on Sunday. Raul Tamudo's goal gave Real Sociedad a 1-0 win over Osasuna in their derby clash. Real Sociedad move up to ninth, while Osasuna drop into the relegation zone as a consequence of Deportivo's win.
Osasuna coach Jose Antonio Camacho is expected to be sacked on Monday.
Julio Baptista and Jose Rondon scored second half goals to help Malaga scrape a 2-2 draw at home to Getafe. Rondon's goal came with the very last kick of the game, but was not enough to lift Malaga off the bottom of the table.
Levante climbed up the table thanks to Felipe Caicedo's second half goal which gave them a 1-0 win over fellow strugglers Almeria.
There was another fightback in Alicante as Hercules recovered from falling a goal down to Zaragoza only for Javier Farinos and David Trezeguet to turn the game around in the last 10 minutes and give the home side a 2-1 win.
Atletico Madrid lost again and coach Quique Sanchez Flores' job is in danger following a 2-1 defeat at home to Valencia.
Jose Antonio Reyes opened the scoring for Atletico after just two minutes, but Joaquin Sanchez equalized with five minutes remaining in the first half. Joaquin scored his second of the game in the closing minutes to take Valencia into third place in the table.
Finally Sevilla's hopes of a top six finish suffered a huge setback as they were beaten 3-2 in Santander by a Racing side that ended up with just 10 players on the pitch.
Christian Fernandez opened the scoring for Racing and Ivan Rakitic doubled the home side's lead after just 18 minutes, before Federico Fazio pulled one back for Sevilla a minute after Christian had been sent off for a foul.
Luis Fabiano equalized with a penalty with eight minutes remaining before Hector Arana sent the home fans wild with the winning goal in injury time.
