Nacional Asuncion coach Gustavo Morinigo was shocked by the substitution of Felipe Gedoz as his side reached the Copa Libertadores final.
The Brazilian had struck the post in the semi-final second leg, which Uruguay's Defensor Sporting won 1-0 to lose the tie 2-1, before being substituted.
Morinigo said the 83rd-minute change had given his team more freedom despite needing to hold on late to avoid conceding again.
"He is very difficult to stop, his shots are very good," Morinigo said of Gedoz.
"He even got one to the post and that was what we were trying to take care of and suddenly his substitution gave us a bit of air and the team started to go forward.
"Even though it wasn't much, but we were able to take advantage and had more freedom because he wasn't on the field."
Striker Fredy Bareiro, introduced late on by the Paraguayans, said his team were excited about their first ever Libertadores final.
Asuncion are likely to face San Lorenzo in the decider with the Argentines leading Bolivar 5-0 heading into their second leg.
"Nobody can takes away from us the dream of being champions of America," Bareiro said.
"So now, with great humility, with great sacrifice, from tomorrow we'll think how the final is going to be.
"Tomorrow we will see who is going to be our rival and with sacrifice and humility we will try to be in the best shape possible for those two games."