Real Sociedad were unable to regain first place in La Liga on Sunday night when they were held to a goalless draw at Basque rivals Alaves.
Deprived of injured captain Mikel Oyarzabal, top scorer in La Liga with seven goals, Sociedad were unable to breach the home defence.
The draw dropped them one point behind Atletico, who on Saturday beat Valladolid 2-0 for a seventh straight Liga victory.
Earlier on Sunday, Villarreal also lost ground with a 0-0 draw at home to Elche. Villarreal regained third place but fell five points behind Diego Simeone's league leaders.
Sociedad and Villarreal have both played two games more than Atletico and one more than fourth-placed Real Madrid.
Real Madrid reversed a recent slide with a 1-0 victory at Sevilla on Saturday.
Promoted Cadiz are fifth after beating visiting Barcelona 2-1 on Saturday, with the troubled Catalan giants dropping to ninth following their fourth league loss of the season.