Real Madrid took advantage of Atletico Madrid's first defeat of the season at Sevilla to move to the top of la liga as Alvaro Morata struck a late winner to secure a 2-1 win over Athletic Bilbao.
Steven N'Zonzi struck Sevilla's winner 17 minutes from time to seal a 1-0 win at a soggy Sanchez Pizjuan on Sunday.
Real lead Sevilla by a point and Barcelona and Villarreal by two at the top of the table.
Atletico, who started the weekend top, slip to fifth, three points back on their city rivals.
Madrid couldn't have hoped for a better start when Enric Saborit's slip allowed Isco to tee up Karim Benzema for a simple finish after just seven minutes.
However, Real's defensive deficiencies surfaced once more when Athletic levelled in scrappy fashion as Javier Eraso's tenacity won the ball inside the Madrid box for Merino to slot home.
Cristiano Ronaldo suffered another off night in front of goal and was even jeered by the Bernabeu crowd when shot straight at Gorka Iraizoz with Isco and Benzema begging for a cut-back for a tap in.
Real were handed a lifeline when Inaki Williams blazed over with just Keylor Navas to beat early in the second period.
Zidane turned to Morata off the bench 15 minutes from time.
And the Spanish international ensured Real didn't drop points at home for a third consecutive la liga game as he bundled Gareth Bale's low cross home at the near post.
Vietto haunts Atletico
Atletico were also left to rue not taking their chances in the first-half as on-loan Atletico striker luciano Vietto came back to haunt his parent club.
Kevin Gameiro shot straight at Sergio Rico and Angel Correa wastefully wide before the break.
Vietto endured a woeful debut campaign at Atletico last season after a 20-million-euro ($21.8 million) move from Villarreal and was used as a makeweight in the deal that brought Gameiro to Atletico in the summer. However, he clipped a fine ball over an uncharacteristically static Atletico defence for N'Zonzi to run through and slot coolly past Oblak.