Barring any final day disasters from Yates, his victory in Spain will mean British riders will have won all three of cycling’s Grand Tours this season.
Team Sky’s Chris Froome won the Giro d’Italia in May, while his team-mate Geraint Thomas won the Tour de France in July.
Stage 20 on Saturday was won by Enric Mas, followed home by Miguel Angel Lopez. The Spanish and Colombian riders climbed to second and third in the overall classifications respectively.
Spain’s Alejandro Valverde began the day second in the overall standings, one minute and 28 seconds behind Yates, but he struggled in Andorra, finishing the day almost three minutes adrift.
Bury rider Yates now holds a 1 min 46secs lead over Mas, with 100.9km standing between him and the Vuelta title.