Jorge Molina opened the scoring inside the first 30 seconds and further goals from Mario and Dorlan Pabon increased Betis' lead before the interval.
The hosts even had the luxury of missing 35th-minute penalty through Molina as they comfortably picked up their first victory in six matches to climb back up to seventh spot on 39 points.
Shellshocked Malaga, who were beaten by Porto in the Champions League in midweek but had not lost in their previous five league outings, could find no way back after that first-half mauling and might have suffered an even heavier defeat after losing Nacho Camacho to a red card in the 63rd minute.
Manuel Pellegrini's side remain fourth in the table but are now just three points above Betis.
Betis had failed to score in 448 minutes of league action coming into tonight's game but they needed less than a minute to end that miserable run after Molina headed home Joel Campbell's left-wing cross at the near post.
Molina almost doubled his account for the night in the 16th minute with an effort Malaga goalkeeper Willy Caballero did well to tip round the post, but the hosts would not be denied a second goal for much longer with Mario netting 10 minutes later.
Benat Etxebarria sent over an inch-perfect cross from the left and Mario climbed above Martin Demichelis to head past Caballero.
It should have been 3-0 soon after but Molina smashed his penalty against the crossbar after Camacho had handled in the area.
Betis need not have worried, though, as their dominant play did earn them a third goal before half-time, Pabon firing home the rebound after Caballero had parried his first effort.
Pellegrini made two changes at the break to try and find a way back into the game, but any hopes the visitors might have had vanished when Camacho was sent off.
The midfielder, having been booked when conceding the first-half penalty, was cautioned for a second time for a foul on Juan Carlos.
After that it was all Betis and only a mixture of poor finishing and good goalkeeping from Caballero kept the hosts from claiming an even bigger winning margin.