The Jaguares host the Australian conference champions at Jose Amalfitani stadium in Buenos Aires on Friday, with the winner to meet either the Canterbury Crusaders or Wellington Hurricanes in the final.
"It's going to be spicy like any semi-final, we are going to have to maintain our concentration and our focus," tighthead Santiago Medrano said.
"They are very strong in the scrum and the maul.
"This is the most important game of my career with the Jaguares," the 23-year-old added.
"I've got a lot of emotions mixed together because the work we've put in the whole year has borne fruit and we are closing in on our objective."
The Jaguares advanced to their first semi-final after they produced a superb defensive effort against the Waikato Chiefs to beat the two-times champions 21-16.
They met the Brumbies earlier this year in Buenos Aires and won a bad-tempered match 20-15.
Young loosehead prop Mayco Vivas also expected a tough battle up front against a Brumbies side whose driving maul is the most lethal in the competition.
Brumbies hooker Folau Fainga'a has been the greatest beneficiary of the tactic with the majority of his team-leading 11 tries courtesy coming from the back of the rolling maul.
"We're expecting a hard and very physical game, a battle between the forward packs," Vivas said.
"They have a great pack, one that is very experienced. The pack, the scrum and the maul, that is going to be key.
"We have been playing very well in the scrum and the defensive maul but we were a bit lax against the Chiefs, although nothing that we can't correct.
"We trust in our defence and in the team. If we defend well then they are going to get frustrated and if they can't get through they give up the ball and they'll get nervous."
(Writing by Andrew Downie; Editing by Ian Ransom)
