Victor, who saved a stoppage-time penalty against Tijuana to secure Atletico's passage to the semi-finals, stopped Maxi Rodriguez's effort after Ronaldinho had put the Brazilian side ahead in the shootout. The tie had ended 2-2 on aggregate.
Tournament favourites Atletico recovered from a 2-0 defeat in last week's first leg in Roasario by beating Newell's by the same score in a match interrupted for 11 minutes late in the second half due to a power failure.
Brazil forward Bernard was quick to reduce the arrears, scoring from a fine Ronaldinho pass after three minutes and substitute Guilherme pounced on a poor clearance with five minutes remaining to make it 2-0 with a long-range shot.
"(Rodriguez) had scored two penalties in the shootout against Boca Juniors and he had hit the first in the corner (of the net) that I went for," Victor said in reference to Newell's quarter-final win over their fellow Argentine side.
"We have to also thank our researchers for passing that information on to me," Victor added.
Atletico will meet three-times South American champions Olimpia of Paraguay in the final over two legs on July 17 and 24.
They will be looking for Brazil's fourth consecutive Libertadores title after victories by Internacional, Santos and Corinthians in the last three years.
"What motivates me to carry on playing is to win unprecedented titles, it makes me feel like a kid again to go on running and doing what I like," an elated 33-year-old Ronaldinho said.
Bernard will miss the first leg of the final through suspension after being booked near the end of the first half for dissent, protesting to the referee for not awarding fellow forward Jo a penalty.
Atletico coach Cuca said the power failure helped him to reshuffle his team, who were struggling to score a decisive second goal against a Newell's side defending well with Rodriguez in fine form in midfield.
"It was good for us because we were being controlled by their marking and we got the chance to change a few things," Cuca said after Guilherme had scored four minutes after he sent him on.
There is no extra time in the Libertadores.