Real coach Juan Ramon Lopez Caro left Ronaldo and David Beckham on the bench in the Bernabeu but it did little to improve his side who laboured to create chances against relegation-threatened Betis.
Barcelona, who beat Real Sociedad 2-0 away on Saturday, have 64 points with 10 games left to play, 11 ahead of second-placed Real. Valencia are third with 52 points.
Betis, who were humbled by Steaua Bucharest in the UEFA Cup during the week, looked the hungrier side in a tight first half littered with misplaced passes, lots of nerves, and few attempts at goal.
Visiting striker Robert almost gave Betis a second-minute lead as Iker Casillas erred coming out of his area, and Real's best chance of the first half came from the foot of Cicinho who's cross-cum-shot hit the far post in the 23rd minute.
After the break, Betis keeper Pedro Contreras blocked a shot from Cicinho with his foot after 65 minutes, and then pulled off a great save from substitute Ronaldo's close-range header six minutes later
Real penned Betis back in the final stages though a swift break from Robert in the 75th minute was only denied by a sharp save from Casillas.
Contreras capped a confident display in the final minute to turn Cicinho's goal-bound shot round the post.
Real were whistled off the pitch at the end by angry home fans.
VALENCIA STRUGGLED
Valencia had not lost in 16 league games but had drawn their last three outings and struggled from the start in Santander.
Racing's Damia Abella burst clear after stealing the ball from defender Carlos Marchena in the 17th minute to grab the opener.
Ayoze Diaz blasted a free kick through the wall to double the lead after 66 minutes, but David Villa pulled a goal back for the visitors from the penalty spot nine minutes later, heading home after the keeper's initial save.
Osasuna strengthened their grip on fourth place with a 4-2 win away to King's Cup finalists Espanyol that put them level with Valencia on 52 points.
The Navarrans beat Barca 2-1 last weekend but fell behind to Raul Tamudo's early strike before fighting back with goals from David Lopez, Pierre Webo and Savo Milosevic before the break.
When Luis Garcia scored a spectacular second for Espanyol midway through the second half, it looked as though the fightback was on.
But the impressive Inaki Munoz cracked in a fourth for Osasuna 10 minutes from time.
Seven points behind Osasuna in fifth place, UEFA Cup quarter-finalists Sevilla squandered a hatful of chances in a 1-1 draw at home to struggling Real Mallorca.
Sixth-placed Celta Vigo, level with Sevilla on 45 points, failed to profit, however, as they went down 1-0 at home to Athletic Bilbao.
At the foot of the table Malaga are bottom with 22 points, Cadiz are 19th with 26, and Betis are 18th with 27, the same as 17th-placed Alaves.