The Welshman sent a left-footed free-kick into the net midway through the first half after Cristiano Ronaldo had opened the scoring with a thunderous strike from over 30 yards out.
Karim Benzema then widened the scoreline even further before the break, taking advantage of a fine move from Luka Modric, and in the second half Angel Di Maria scored his second goal in as many games before substitute Alvaro Morata piled further misery on Liga whipping boys Betis.
The Andalusians have taken just one point in six league games under Juan Carlos Garrido, who succeeded Pepe Mel - now in charge at West Bromwich Albion - at the start of December, and speculation has been growing that Betis' directors are planning on changing coach yet again.
Betis took all three points against Jose Mourinho's Madrid in last season's fixture, but with 36 points separating the two teams in the league table before the match, few would have expected a repeat result.
And although the hosts made a positive start, with Ruben Castro having the first shot on target, Ronaldo soon killed off any hope they might have had by scoring arguably his best goal of the season with 10 minutes gone.
The newly crowned FIFA Ballon d'Or winner received a short pass from Di Maria on the left hand side of midfield, brought it further infield and shook off a challenge from a Betis defender before blasting the ball into the top corner to score his 21st league goal in 20 appearances.
Betis' heads did not drop immediately after going behind and they retained possession and got forward without causing Madrid goalkeeper Diego Lopez any problems.
But as soon as they relinquished the ball they were vulnerable to Madrid's breath-taking counters.
Ronaldo burst into the box on one such break but saw his effort go over the bar, but he then won the free-kick which resulted in Bale scoring a much-needed goal.
The Welshman had been unable to find the net since scoring a hat-trick against Valladolid on November 30 but sent the ball dipping over the wall and past Stephan Andersen, who barely twitched before picking the ball out of the net.
Twenty minutes later, Madrid produced another exquisite goal.
Modric entered the box from the left side and used fine footwork to glide past three Betis defenders and lay the ball off to Benzema, who slotted into the near corner.
Betis all but surrendered after the break, and Di Maria hit the fourth goal of the afternoon just after the hour mark, sending the ball low into the bottom corner from 35 yards following a corner.
And in injury time Morata converted a cross from Marcelo at the far post to complete an emphatic win.