Atletico – who hold the edge on Real Madrid on a head-to-head basis – moved level on points with their neighbours at the top of the Liga table after second-half strikes from Gabi and Diego Costa gave them their 10th away league win of the season.
If Atletico and Real end the campaign on the same number of points, Diego Simeone's side will finish higher because of their win and draw garnered from the two derby meetings this term.
They were made to work for their latest victory, but eventually their quality shone through against bottom-placed Betis, just two hours before Real's much-anticipated clash with third-placed Barcelona at the Bernabeu.
Costa had a goal ruled out for offside in the first half, a decision that appeared to be harsh, but the match swung in Atleti's favour when Braian Rodriguez was sent off for a second yellow card in the 56th minute.
Gabi capitalised with a stunning 25-yard strike just two minutes later, and Costa then showed his predatory instincts with a clever left-foot finish just after the hour as struggling Betis' slim chances of survival took another blow.
The first half's main talking point almost immediately followed, as an unlucky Costa had a goal cancelled out.
Raul Garcia then missed a sitter, after Costa's lay-off, and was immediately substituted, but his strike partner netted a second, reacting to Koke's flick-on header with a fine finish for his 23rd Liga goal of the season.
