The twice champion Brumbies stand between the Argentine outfit and a place in the final in only their fourth season in the competition when the teams meet at the Jose Amalfitani Stadium on Friday.
The South African conference champions beat the Brumbies 20-15 in Buenos Aires in late April but the Australian team have not lost since and go into the clash on a seven-game winning streak.
"Ever since that game they have gelled as a group and have reached the semi-finals," de la Fuente told reporters at the captain's run on Thursday.
"They have clearly gotten better. They have much more confidence. We really need to grit our teeth and play the perfect game."
Where once Australian sides were feared for their running game, de la Fuente said the Jaguares were more concerned about containing the Brumbies pack.
"They have a great defence, the best in the tournament, and a tremendous maul," the Pumas centre added.
"I think it is the team that has scored most tries from the maul, that's their weapon.
"We remember the game we played here and we made a mistake in their half and they took strength from that.
"We have to take strength in our defence and get the ball."
While the Jaguares are one of the youngest teams in the competition, the Brumbies are Australia's most successful Super Rugby side and will be contesting their 10th semi-final on Friday.
De la Fuente said his scrumhalf Tomas Cubelli, who played for the Canberra-based side in 2016 and 2017, had given Jaguares an insight into the culture at the Brumbies and he felt the two clubs had similarities.
"It's a team I've been watching since I was a boy," de la Fuente said.
"The history of Australian rugby is there, they have a spirit very like ours. The Jaguares and the Brumbies are very similar in a spiritual sense.
"Cubo knows them and has told us about them. You'll see that out on the pitch, it's going to be quite a game."
The Canterbury Crusaders host the Wellington Hurricanes in the other semi-final in Christchurch on Saturday.
(Writing by Andrew Downie, editing by Nick Mulvenney)
