Juan Luis Morales’s volley went into the net off the legs of Betis keeper Casto Espinosa in the 33rd minute and from there on their rugged defence held firm to maintain their unbeaten start to the season.
Barcelona later beat Sporting Gijon to join Levante on 14 points, but the European champions are top of the table on goal difference.
Sevilla went sixth with 11 points, one behind their city rivals Betis in fourth, after a 0-0 draw at Atletico Madrid thanks to the efforts of goalkeepers Javi Varas and the home side’s Thibaut Courtois.
In the midday kickoff, Real Sociedad’s Inigo Martinez scored from inside his own half in the Basque derby, but Fernando Llorente’s brace made sure Athletic Bilbao earned a 2-1 win at the home of their north-coast reivals.
Centre back Martinez let fly from over 50 metres out catching Gorka Iraizoz off his line, the visiting keeper perhaps distracted after one of his defenders had just been carried off on a stretcher, and the ball dipped under the bar.
Spain striker Llorente had put Bilbao ahead, turning in the area to score in the 34th minute, before Martinez levelled just past the hour mark in a sun-soaked San Sebastian.
Llorente then struck a superb volley to restore Bilbao’s advantage in the 71st minute and earned under-pressure Argentine coach Marcelo Bielsa a first league win this season.
Bilbao climbed out of the bottom three to five points from six games, two behind their hosts in ninth.