Banfield suffered their first loss of Argentina's Apertura championship on Sunday, losing 2-1 at home to Racing Club, who continue their revival under the guidance of coach Claudio Vivas.
Defender Matias Martinez put Racing ahead with an early goal but Banfield's Uruguayan striker Santiago Silva headed an equaliser after just 16 minutes to remain as the championship's top scorer this season, with 13 goals.
Left back Gabriel Mercado then struck the winner for Racing just after the hour, ending Banfield's 15-match unbeaten streak this campaign.
Banfield, a club looking to lift their first league title, remain at the top of the championship standings by two points but could drop back to second if their nearest rivals Newell's Old Boys beat third-placed Colon away in Santa Fe on Monday.
Club World Cup-bound Estudiantes missed their chance to go up from fourth to third place when they conceded a last-gasp goal to former Argentina forward Ariel Ortega in a 1-1 draw with River Plate on Saturday.
Title holders Velez Sarsfield climbed into fifth spot with a won 3-0 away win over bottom-placed Tigre on Sunday, with Chile's Waldo Ponce scoring twice and Argentina's Emiliano Papa once.
Boca Juniors remain mid-table after they were beaten 3-0 at San Lorenzo on Sunday.