The Crusaders scored three contentious tries to beat the Chiefs 28-21 in Super Rugby on Friday night, threatening the Chiefs' lengthy tenure atop the standings while firming their own playoffs bid.
The Chiefs entered the match four points ahead of the Cape Town-based Stormers but their third loss in 15 matches offered the South Africans the chance to move into first place if they can take a bonus-point win from their match against the Cheetahs on Saturday.
Canterbury opened a 20-6 lead with first-half tries to back-rower Kieran Read, who appeared to lose the ball over the line, and lock Luke Romano, who may have been offside.
But the Chiefs gradually battled back, finally managing to break the Crusaders line as the half-hour mark neared when second-rower Brodie Retallick latched onto halfback Tawera Kerr-Barlow's beautifully timed pass five metres out.
Cruden added the extras and another penalty as halftime neared cut the Crusaders' lead to 20-16 at halftime.
Ellis extended the lead 10 minutes into the restart when the video referee ruled he had been shunted over for the Crusaders' third try, but it only took the Chiefs four minutes to respond.
Kerr-Barlow made the initial break from a turnover before Sonny Bill Williams showed superb strength in the tackle to touch down and narrow the gap to four.
A 62nd minute Carter penalty stretched it back out to seven, but the Crusaders' defence was tested to the limit for the rest of the match.
CRUSADERS 28 (Andrew Ellis, Kieran Read, Luke Romano tries Daniel Carter 2 cons 2 pens drop goal) bt CHIEFS 21 (Brodie Retallick, Sonny Bill Williams tries Aaron Cruden con 3 pens) at Waikato Stadium. Referee: Steve R. Walsh