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Rayo substitute Fran Perez thrashed home a 67th-minute equaliser as he stole in unmarked at the back post from a corner after Lamine Yamal’s 40th-minute penalty had put Barca ahead.

A malfunctioning VAR ensured the game was clouded in controversy after Pep Chavarria's challenge on Yamal, which led to the spot kick being awarded, could not be reviewed because the system was not working at the time.

Chavarria did make contact with Yamal’s thigh but the penalty award might have been overturned on review.

Both teams had been informed of the faulty system at kick-off, but Rayo’s vigorous protests over referee Mateo Busquets’ decision ensured the rest of the clash at Estadio de Vallecas was played in a tempestuous atmosphere.

Indignant home supporters voiced their fury at every subsequent decision that went against their side.

Barcelona goalkeeper Joan Garcia made several outstanding stops to deny Rayo a win at the end of a week in which the club from the Madrid suburbs secured a place in the Conference League group phase on its return to Europe after 24 years.

García made a point-blank save to deny Andrei Ratiu in the 12th minute and in the second half spectacularly denied efforts from Isi Palazon and a breakaway on goal by Jorge de Frutos.

Substitute Sergio Camello could have won the game for Rayo in the last minute but, with the goal at his mercy, he miscued his shot, allowing a grateful Garcia to gather easily.

For Barca, Daniel Olmo was guilty of missing a sitter soon after teenager Yamal’s penalty had put the visitor ahead. He hit the ball over the top of the crossbar from close in, setting off an angry reaction from furious coach Hansi Flick.

Barcelona had won its opening two games of the season but the dropped points mean Real Madrid and Athletic Club are the only two clubs with a 100 percent record after three matches. Rayo has four points from its opening matches of the campaign.