Saturday night's 40-16 win at Waikato Stadium in Hamilton saw the Chiefs' late blitz break open the game and confound those expecting the latest tense chapter in this intriguing rivalry.
The Chiefs' five tries marked the most they had managed in 20 seasons of clashes with the Crusaders.
And to top it off for the two-time champions, the 24-point winning margin was another record against the red-and-blacks.
And Rennie was right - the spanking was relatively rare for his tenure. He is now in his fourth season in Hamilton and the Chiefs had previously enjoyed only three victories by more than 20 points, each against South African opposition.
Adding further to the improbability of the result, the Crusaders hadn't leaked 40 points in that same three-year timeframe, with Saturday surpassing the 35 they conceded last year against the Blues.
Whatever the measure, it was a comprehensive triumph that maintained the Chiefs' early unbeaten streak.
But Rennie, never one to get carried away, emphasised just how early it was and still found fault in his side's performance.
"It was a step in the right direction," he said. "We weren't very happy with the last 15 minutes and the quality of our finishing - we had opportunities where we should've scored again.
"You want those guys coming off the bench to give impact. They gave us plenty of enthusiasm but we just lacked a little bit of polish."
Perhaps that was also the Chiefs' perfectionist nature shining through, content with the five points that left them level with the Hurricanes but instantly seeking improvement ahead of Friday's visit of the Highlanders to the Tron.
As well as amending certain areas, much of the immediate focus will surround the health of Brodie Retallick.
The reigning world player of the year lasted only 10 minutes in his first start of the season, succumbing to injury before being substituted.
Retallick has a suspected AC shoulder joint problem, with the severity to be assessed over the coming days. It could keep the lock on the sidelines for a number of weeks but, with a trip to South Africa looming for the Chiefs, Rennie wasn't about to count him out of the reckoning yet.
"He's pretty resilient, Brodie, and he tends to bounce back pretty quickly, so it wouldn't surprise me to see him on that plane."