Striker Aritz Aduriz scored two goals to help Athletic Bilbao win 2-1 at Levante on Monday, strengthening the Basque side's hold on fourth place in the Spanish league.
Bilbao's second victory in six games restored their six-point advantage over fifth-place Sevilla.
"Today was a very important game because all the rest of the way the games will be like this," said Bilbao coach Ernesto Valverde. "Sevilla, Real (Sociedad), are coming on strong. It will be tough from here on in."
Bilbao defender Mikel San Jose missed a chance to grab the lead in the 12th minute when he misfired a penalty after Juanfran Garcia fouled Iker Muniain.
But Aduriz struck three minutes later when his shot took a deflection off a defender to catch goalkeeper Keylor Navas out of position.
Bilbao continued to dominate both possession and scoring chances, and Aduriz hit again by heading home Ander Herrera's well-placed cross just before halftime.
Aduriz's double gave him a team-leading 13 goals in the league this season.
San Jose compounded his erred spot kick by scoring an own goal in the 66th when Ruben Perez's cross hit his leg and looped into the net.
Bilbao lost midfielder Mikel Rico to injury in the first half after Victor Casadesus hurt his ankle with a low tackle.
Atletico Madrid leads the league by one point over Barcelona. Real Madrid is another two points behind with six rounds to play.