The visitors got off to the worst possible start as keeper Casto was sent off after just 11 minutes for bringing down Eliseu inside the area and Joaquin confidently stroked home the penalty.
Javier Saviola then continued his great form with the second just before the half-hour and the hosts' fine afternoon was rounded off in the final 20 minutes when Antonio Amaya could only direct Nacho Monreal's cross into his own net before Isco dinked in the fourth moments later.
Betis had felt extremely let down by refereeing decisions as they had two players sent off and conceded a penalty against Atletico Madrid in midweek, and manager Pepe Mel's mood was not improved any when Casto was deemed to have denied a clear goalscoring opportunity when he brought down Eliseu as the Portuguese tried to round him.
As a result Adrian replaced Salvador Agra to make his La Liga debut, but his first job was simply to pick the ball out of the net as Joaquin sent him the wrong way from the spot.
Soon after, though, Adrian did well to deny Eliseu a second and Nacho Camacho then saw a header come off the post from Joaquin's free-kick.
But when the second goal did arrive there was again a touch of controversy about it. Great combination play between Isco, Saviola and Francisco Portillo freed the latter on the right side of the box but he appeared to be in an offside position as he squared for Saviola to tap in his third goal in five games for Malaga.
The hosts remained completely dominant after the break and were only denied a third before the hour mark by a remarkable goalline clearance by Nacho as he scrambled away Martin Demichelis' effort from point-blank range.
Ruben Castro then had the visitors' best chance of the afternoon as he accelerated through on goal but when Weligton got back to block his effort, any hope of a remarkable comeback was extinguished and Malaga went on to consolidate their advantage in the final quarter.
Firstly, Amaya could only turn Monreal's wicked delivery into his own net on 72 minutes before Roque Santa Cruz put Isco through to delightfully chip in the fourth two minutes later.