Robert Lewandowski's first-half penalty secured a gritty 1-0 win for Barcelona over Rayo Vallecano on Monday, propelling them to the top of La Liga.

Barça capitalized on slip-ups from Real Madrid and Atletico Madrid over the weekend, climbing from third to first. They sit level with Real on 51 points but hold the edge on goal difference.

Atletico lurk just a point behind, while in-form Rayo Vallecano remain sixth with 35 points.

Barcelona did just enough to snap Rayo's nine-match unbeaten streak in the league, leaving the visitors fuming over several controversial referee decisions.

After Pathe Ciss fouled Inigo Martinez inside the box, Mario Melero Lopez awarded the home side a penalty following a lengthy VAR check.

Lewandowski netted the winner with a tidy finish from the spot in the 28th minute.

Despite Barcelona dominating possession, Rayo looked the more dangerous side, forcing goalkeeper Wojciech Szczesny into a brilliant performance to keep them at bay.

Rayo players were outraged when their pleas for a penalty were turned down after Pau Cubarsi appeared to foul Ciss – an incident they felt mirrored the one that led to Barcelona’s spot kick.

Their frustration grew when Jorge de Frutos' goal was controversially ruled out in the 42nd minute.

Defender Martinez made a crucial goal-line clearance with his head right before the break, while Szczesny continued his heroics in the second half to help secure the three points.

Rayo squandered a golden chance to equalize when De Frutos missed a close-range header in stoppage time.

"I prefer to keep my opinion about the referee to myself, but everyone acts as they believe they should," a visibly frustrated Rayo manager Inigo Perez told Movistar Plus when asked about the controversial calls.

"You always feel the pain of losing, but today it will take a few hours for me to calm down, considering everything that happened and the way we played. At the moment, the only word I can find is bitterness."