Under pressure from its closest challenger, FC Barcelona stumbled again. Barcelona couldn't manage more than 1-1 against relegation-wary Las Palmas on Thursday, allowing Atletico Madrid to move within five points of the Spanish league lead ahead of their match this weekend.
Barcelona, which has drawn three of its last five league matches, will host Atletico on Sunday needing to halt an eight-match winning streak by Diego Simeone's team.
Barcelona was 11 points in front of Atletico just five rounds ago, but could end the weekend only two points in front of the Madrid club.
The Blaugrana faces stiff competition from the Premier League defending champions Chelsea as they drew the first legt at Stamford Bridge.
"It would be an important match no matter what, with the first-place team playing against the second-place team," Barcelona coach Ernesto Valverde said. "Maybe now it's a bit more important with the lead at five points."
Atletico was boosted by a 4-0 win over Leganes on Wednesday, when Antoine Griezmann scored all four goals.
Lionel Messi put Barcelona ahead on Thursday with a powerful free kick shot into the top corner in the 20th minute, but the hosts equalized through a penalty kick converted by Jonathan Calleri early in the second half after a controversial handball by Barcelona defender Lucas Digne.
At first it wasn't clear why the penalty was called. A corner kick ricocheted off a post and the ball brushed Digne's arm. Some Barcelona players initially thought the referee called a foul by Sergio Roberto on Matias Aguirregaray when the ball first arrived into the area.
Valverde said he and his players still didn't know what the call was.
"They equalized after an invisible penalty," he said.
Barcelona also complained about a non-call of handball by Las Palmas goalkeeper Leandro Chichizola outside the area just before halftime.
It was the fifth free-kick goal by Messi, who is the league-leading scorer with 23, three more than teammate Luis Suarez. The Argentine playmaker has four goals in his last three matches. The Gran Canaria Stadium was one of the few venues where Messi was yet to score in La Liga.
Las Palmas stayed 18th in the 20-team standings, inside the relegation zone. The team from the Canary Islands has won only one of its last six matches.