Nacional extend Uruguayan title decider
As the team that finished top of the overall standings, Defensor would have lifted the title if they had won the decider forced by 1-1 draws in both legs of the original final.
However, the victory earned Nacional, who qualified to challenge for the title after winning the Clausura championship in the second half of the season, another shot.
The complex format means the teams will now play another final with the first leg on Sunday and should they draw again, another one-off decider will be played but the winner of that game would be crowned champions.
Defensor could have taken the lead on Wednesday hen they were awarded a penalty in the seventh minute but Diego De Souza's spotkick was saved by Rodrigo Munoz.
A Santiago Garcia penalty put Nacional in front after half an hour.
Defensor had De Souza sent off on the hour for a bad foul on defender Sebastian Coates before Nacional added two more goals in the final 16 minutes though Coates and midfielder Alvaro Fernandez.