Martinez’s late goal seals a 2-1 win for Athletic over Atletico. Berenguer gave the hosts an early lead when he sent his diving header past Oblak.
Atletico improved in the second half without having a shot on target until Savic nodded in Carrasco’s corner to equalise.
Athletic pulled it back though and Martinez thumped a header past Oblak from a corner to earn the three points for his side.
Atletico miss the chance to go five points clear at the top of LaLiga and are now just two points ahead of Barcelona and Real Madrid with only five games left.
We’re devastated,’ said Atleti captain Koke. ‘We looked to get back in the game in the second half by any way possible, we drew level then they got the winner from a set piece.
‘We just have to keep going and try to win our next game, we badly need to do that.’
Atletico’s defeat adds extra intrigue to a thrilling four-way title race, with three points separating them and fourth-placed Sevilla, who beat Granada 2-1, with five games left.
Champions Real Madrid are second after being held to a 0-0 draw at home to Real Betis on Saturday. Atletico visit struggling Elche next before a blockbuster game away to Barcelona on May 8.
Atletico still lead the table on 73 points but third-placed Barca, on 71 after beating Villarreal 2-1 earlier on Sunday, can go clear at the top if they beat Granada on Thursday.
They’re winless in four on the road which Simeone will be hoping to change when they travel to Elche next time out.
Athletic end their eight-match winless run, with Real Valladolid next for them.