The Crusaders kept their Super Rugby title hopes alive by beating the tournament leading Chiefs 21-28 at Waikato Stadium in Hamillton.
The Chiefs had already qualified for the Super Rugby finals and won the New Zealand Conference but the Crusaders had to win this week to stay in contention following their loss to the Hurricanes last week.
The Chiefs started the match four points ahead of the Stormers from Cape Town but their third loss in 15 matches gives the South African side the opportunity to move into first place if they can take a bonus-point win from their match against the Cheetahs on Saturday.
The Crusaders outscored the Chiefs by three tries to two but failed to score the bonus point try while the Chiefs picked up a losing bonus point for finishing within seven points.
The Chiefs play the Hurricanes next weekend and they will be hoping to secure a home semi-final while the Crusaders will host the Western Force in Christchurch.
Defeat would have left the Crusaders, losing finalists to the Reds last year, reliant on other results to make the top six.
The Crusaders returning All Blacks stars Dan Carter, Israel Dagg and Kieran Read were pivotal for the Crusaders.
The loss is a blow to the Chiefs chances of securing a top two position, which would have guaranteed a home semi-final.
But the Waikato team, who boast former All Blacks assistant coach Wayne Smith as part of their backroom staff, can finish no lower than third and remain well placed in their quest for a maiden Super rugby title.
The Chiefs came out firing, Aaron Cruden and Tawera Kerr-Barlow combining to put them within five metres of the tryline in the first minute, but having to settle for three points after a penalty to the Crusaders.
Carter evened the score with a penalty two minutes later before Kieran Read, profiting from early Crusaders dominance in the scrum, latched onto a short pass from Israel Dagg for the first try, which was converted by Carter.
Both sides continued to throw the ball around in a ferociously contested match, with Carter, once known for his aversion to drop goals, putting the Crusaders up 13-6 with a field goal from open play after 17 minutes.
Luke Romano followed up with a try from a rolling maul as the South Island team's forwards continued to monster the Chiefs, which Carter again converted to make it 20-6.
With the Crusaders threatening to run away with the match, Brodie Retallick hit back for the Chiefs when Kerr-Barlow sold a dummy pass to the defence, leaving a clear path for the young lock.
Cruden converted and scored another penalty to narrow the gap to 20-16 in the Crusaders' favour at half-time.
He sliced a penalty attempt just after the restart but the Crusaders again grabbed the initiative after Andy Ellis scored a try, despite Chiefs' protestations Kerr-Barlow had held up the ball on the line.
Former rugby league star Sonny Bill Williams, who was missing in action for much of the first half, kept the Chiefs in it, bludgeoning his way through three defenders for the Chiefs' second try, Cruden adding the extras.
In the final 20 minutes, Carter slotted a penalty and the Chiefs had a try to Asaeli Tikoirotuma disallowed, with the home side enjoying attacking chances but let down by a misfiring line-out.
The Chiefs opted to run the ball after being awarded two penalties following the siren, with Sonny Bill Williams adjudged held up over the line after the second to give the Crusaders a win.
Final Score Chiefs 21 (16) Crusaders 28 (20)
Tries - B. Retallick, SB. Williams
Pen - A. Cruden 3
Con - A. Cruden 1
Tries - K. Read, L. Romano, A. Ellis
Pen - D. Carter 2
Con - D. Carter 2
Drop - D. Carter
Referee: Steve Walsh
Assistant Ref 1: Garratt Williamson
Assistant Ref 2: Glen Jackson
TMO: Bryce Lawrence
1. Ben Franks, 2. Corey Flynn, 3. Owen Franks, 4. Luke Romano, 5. Samuel Whitelock, 6. George Whitelock, 7. Richie McCaw (c),8. Kieran Read, 9. Andy Ellis , 10. Dan Carter (vc), 11. Zac Guildford, 12. Ryan Crotty, 13. Robbie Fruean, 14. Adam Whitelock, 15. Israel Dagg.
Replacements: 16. Quentin MacDonald, 17. Wyatt Crockett, 18. Tom Donnelly, 19. Matt Todd, 20. Willi Heinz, 21. Tom Taylor, 22. Sean Maitland.