Long-awaited victory in Super Rugby's southern derby has put the Highlanders squarely in the playoff picture, while delivering a crippling blow to the hopes of the defending champion Crusaders at Dunedin.
The 32-29 win has shattered a 19-game losing run against NZ franchise teams and may have secured their own place in the competition post-season, with probably their best performance of the season.
Growing in confidence, first-five Cam Millar scored 27 of his team's 32 points, with a faultless kicking performance and a first-half try, backing up halfback Folau Fakatava near the line.
By contrast, their rivals may have seen their title defence coming to an end, with top Aussies ACT Brumbies and top-of-the-table Blues next on their schedule.
The Crusaders welcomed back All Black front-rowers Tamaiti Williams and Codie Taylor, but suffered an important loss on gameday, with the late withdrawal of captain Scott Barrett, who had suffered a back niggle seven days earlier and sat again as a precaution.
The home side started strongly and Millar drew first blood with a penalty from in front.
They also had the first try, when a Crusaders pass in midfield deflected off the head of No.8 Nikora Broughton in a tackle, and centre Taniela Tele'a gathered to race away and score.
From the kickoff, Crusaders halfback Noah Hotham ran deep into the Highlanders 22 and was not released by counterpart Fakatava, who earned 10 minutes on the sideline. From the attacking lineout, first-five David Havili threw a long pass for winger Sevu Reece to score.
With Fakatava still serving his yellow card, Millar soaked up a few previous seconds with another close-range penalty.
Crusaders flanker Cullen Grace loomed in support of centre Levi Aumua and dived over in the corner, but his try - initially awarded - was rubbed out, when replays showed he grounded on the touch-in-goal line.
From the 22 dropout, fullback Johnny McNicholl broke back into the 22 and Hotham went within metres of the line, before offloading for second-five Dallas McLeod to score.
Restored to full strength, the Highlanders went back on the offensive, with Fakatava finding Millar on his shoulder for a try. Millar slotted another penalty and the margin was widening.
When Broughton burst upfield, flanker Sean Withy was held up over the tryline, but Millar banked another three points from the penalty.
From a scrum on halfway, winger Timoci Tavatavanawai was unleashed down the right sideline and after 18 phases, the Crusaders lost lock Jamie Hannah for a no-arms tackle on the goal-line.
With halftime looming, the home side squandered a series of chances to add to their advantage and they returned to the changing room with a 26-14 lead.
Seconds before Hannah was due back from his yellow card, the Crusaders struck a potentially important blow, when they won an attacking lineout and shifted left, where Reece snagged his second try. Winger Chay Fihaki further reduced the deficit with a penalty from in front.
The visitors seemed to have gained some momentum, but could not turn that initiative into points, as defence dominated for both sides.
Eventually, Millar restored a seven-point lead with a penalty seven minutes from the end and then put it beyond reach with another.
As the final siren sounded, Millar was yellow-carded for a cynical offside on his goal-line, as the Crusaders tried to salvage a bonus point, and eventually replacement Macca Springer scored in bizarre circumstances, when defenders were told to release him in a tackle and he simply fell over the line.
The visitors had scored four tries to two, but could probably blame indiscipline - along with the Highlanders' strategy of kicking for goal - for their defeat.
The southerners now sit seventh, nine competition points clear of Moana Pasifika and the Crusaders in ninth and 10th, which means their rivals must win at least two of their last three games each - with some bonus points - to deprive them progress to the playoffs.
Moana have the Hurricanes and NSW Waratahs, before meeting the Crusaders to finish the regular season.
"Extremely proud of the boys," said de Groot. "I've got to put it down to those massive [defensive] sets, the boys never gave up.
"It's just important we don't get too big for our boots - we just take each week as it comes. We'll just keep doing what works well, which is working hard, getting stuck into teams, climbing into rucks.
"That's Highlanders footy, we love it."
The Crusaders are still only three points adrift of eighth-placed Fijian Drua, so one win may yet be enough to grab a place in the quarter-finals, but the Drua have two of their last three games against Queensland Reds and Melbourne Rebels at their Lautoka fortress.
"We let in a few points in that first half against the 'Landers, who get a bit of confidence from that on their home ground, and it's hard to claw your way back," admitted Taylor. "I thought we played quite well when we had the ball in the first half, but then lost our way in the second."
The Crusaders visit the Brumbies at Canberra next Saturday, while the Highlanders travel to Auckland to face top-of-the-table Blues for the Gordon Hunter Trophy.
Highlanders 32 (Tele'a, Millar tries; Millar 6 penalties & 2 conversions) Crusaders 29 (Reece 2, McNicholl, Springer tries; Fihaki 3 conversions & penalty)
