MADRID, Jan 15 (Reuters) - Barcelona marched on to their 17th consecutive victory in all competitions on Sunday, coming from behind to beat Athletic Bilbao 2-1 at home in the Primera Liga.Ronaldinho scored from the penalty spot in the 36th minute and Argentine forward Leo Messi added the second in the 51st minute after Bilbao, who made like difficult for the champions, had taken an early lead through Fernando Llorente. Barca had Portugal midfielder Deco sent off in the final minute. The win confirms Barcelona as the clear leaders in Spain at the halfway point of the season, as they hold the top spot with 46 points, seven ahead of second-placed Osasuna. The Navarrans fell 2-0 away at third-placed Valencia on Saturday, who look like the side currently most likely to mount a challenge despite being 10 points adrift. Real Madrid moved up to fourth on 33 points after a Zinedine Zidane hat-trick helped them overcome Sevilla 4-2 in the Bernabeu later on Sunday. Real captain Guti got the home side off to a flying start with an early goal, though Fabiano brought the Andalucian side level just after the break. Two classy Zidane strikes moved Real clear, though Aitor Ocio punished a mistake by goalkeeper Iker Casillas to ensure a nervy finish. But Zindane's third - completing his first hat-trick for the club - gave the home side the points. Bottom club Alaves surprised fourth-placed Deportivo Coruna with a 2-0 away win to give new coach Juan Carlos Oliva a win in his first game in charge. Fifth-placed Villarreal missed a penalty and had a player sent off on their way to a 1-0 defeat at nine-man Racing Santander. Alaves are kept at the foot of the table with 15 points on goal difference by Bilbao. Hector Cuper's Real Mallorca, on 17 points, occupy the third relegation spot after going down 3-1 away to in-form Real Zaragoza. Bilbao set their stall out defensively with five across the back but were quick to break when the opportunity arose and took the lead after 15 minutes. A short corner allowed midfielder Fran Yeste to whip in a cross from the right which Llorente nudged into the far corner with a flicked header. Barca were rattled and after 21 minutes Bilbao winger Joseba Etxeberria broke clear on a counter but Victor Valdes got down well to his shot. The pressure from the home side paid off after 36 minutes when defender Fernando Amorebieta handled in the area, and Ronaldinho made no mistake from the spot. The Catalans stepped up a gear after the break and the second goal arrived in the 51st minute when Mark van Bommel's shot was only parried by Inaki Lafuente and Messi rolled the ball into the empty net. Van Bommel crashed a shot against the upright soon after but the home side were frustrated by Bilbao. Tempers flared at the end and Deco over-reacted to Carlos Gurpegi's provocation to see red. Television cameras also caught Samuel Eto'o spitting in the face of Bilbao defender Unai Exposito.