Racing remain one point in front of Nacional atop the Apertura table but were made to work for their latest triumph on Saturday.
Tacuarembo entered the match having lost three of their last four but were resolute in defence, frustrating their more-fancied opponents.
And Racing looked like failing to score for the first time since March until Franco Sosa's unfortunate 90th-minute own goal.
Nacional won far more easily – Carlos De Pena's first-half double gave them a 2-0 win at Atenas on Sunday.
Rentistas are three points behind Racing after a comfortable 3-0 triumph at Danubio, also on Sunday.
Ignacio Ithurralde gave Rentistas the lead in the 44th minute and further strikes from Hugo Soria and Federico Laens sealed their triumph.
Penarol lost further ground on Racing despite maintaining their unbeaten record this season, a third successive draw leaving them four points off the pace.
Penarol, who could reach the Copa Sudamericana's last 16 with victory at Colombia's Deportivo Cali on Wednesday, had to come from behind to win a 1-1 draw at El Tanque Sisley.
Juan Manuel Olivera scored their equaliser with seven minutes to play.
At the other end of the table, rock-bottom Cerro ended a run of five losses with a goalless draw at Sud America.
Cerro are still two points adrift of Atenas.
Elsewhere, Defensor Sporting extended their unbeaten run to four with a 2-0 win over Juventud.
River Plate ended a run of two losses with a 3-1 success against Fenix, while Rampla Juniors won 1-0 at Wanderers.
