Desperation not to rest on their laurels. Desperation to work hard. Desperation to succeed. Desperation to retain the Super Rugby title.
That desperation was never more evident than when fly-half Aaron Cruden, the smallest man on the field, tracked back and made a try-saving tackle in their semi-final victory over the Canterbury Crusaders last week.
Nor than in the way All Blacks lock Brodie Retallick cleaned out Corey Flynn during a ruck, driving the Crusaders hooker back two metres.
Nor than when hooker Hika Elliott lasted the entire 80 minutes of test-intensity rugby against the seven-times champions despite having been on a drip as late as Thursday after suffering food poisoning during the week.
"The boys have worked really hard and they have an understanding of how hard it is to win a championship," Rennie told Reuters.
"We were really focused on ensuring there was the same sort of desperation leading into this season otherwise it's quite easy to think you have climbed a mountain and then not work as hard and achieve the same sort of success.
"It's a tough competition. Lot of travel and you're playing against some of the best sides in the world.
"We're just rapt to still be here and preparing for another game."
Shorn of major drawcard Sonny Bill Williams and injured All Blacks centre Richard Kahui, the Chiefs started the competition with a 41-27 demolition of the Otago Highlanders, a team that many had predicted would be title challengers.
Rennie's side suffered a mid-season blip with losses to the Queensland Reds and New South Wales Waratahs which coincided with an injury crisis in midfield that had the coach seeking a short-term contract for former Crusaders centre Casey Laulala.
Fortunately, that crisis has now passed and Andrew Horrell is back at inside centre to offer another kicking option against the Brumbies alongside that of the increasingly influential Cruden.
"We can bring guys off the bench if we need to change the game but Andrew Horrell is a smart footy player," Rennie said.
"He may be not as quick or evasive as others but he is smart and has the ability to get the ball out of his hands or put the right sort of kick in, based on what he sees, and I think that will be important at the weekend."
The Chiefs shook off the losses to the Australian sides with six successive victories before the international break in June, although when they returned they were hammered by the Crusaders 43-15.
Assistant coach Wayne Smith called it the most pressure the team had been under in the 18 months of Rennie's tenure and it shook them out of complacency.
They responded in the semi-final last Saturday.
While the Chiefs had more recent experience than Jake White's side in the playoffs - the Brumbies last played in a final in 2004 - Rennie saw danger in the Canberra-based side in their victory at Loftus Versfeld last week.
"They play a lot of territory and don't tend to play too much footy down their end of the field," Rennie said.
"Then they really strangle you down your end of the field and that's where they're pretty lethal."