The Crusaders have scored a single try in each half to beat the Blues 15-3 in an edgy, pivotal match in Super Rugby Pacific.
The face-off between the fourth-placed Blues and fifth-placed Crusaders was much-anticipated and watched by a capacity crowd of 17,000 in Christchurch.
But while it was physically intense, it provided little in terms of points.
The Crusaders - who rose to third on the ladder with victory - dominated possession, especially in the first half when the few shreds the Blues obtained were kicked away by five-eighth Beauden Barrett.
Possession evened out to about 60-40 in favour of the Crusaders after the break but they retained the advantage in terms of territory, with the Blues unable to marshal a coherent attack.
The Blues' defence stayed solid, not least during a 20-minute period in the second half when their captain Dalton Papali'i was red-carded for a high tackle on Crusaders five-eighth Richie Mo'unga.
They did not concede a point in that period but they missed around 25 tackles overall and that was crucial as the Crusaders punched through midfield with big ball-carrying forwards.
Beauden Barrett set in motion an end-to-end kick-and-chase late in the match but it was shut down on the try line by Crusaders fullback Will Jordan.
"The game was won with our defence," Crusaders captain Scott Barrett said.
"To hold them to three points was a huge testament.
"At times it was a bit ugly and we didn't fire too many shots but we closed down their game and a lot of their firepower didn't get into the game."
Thirty minutes passed before the first points came with a try to Crusaders backrower Quinten Strange.
Barrett kicked a penalty and Mo'unga another and that ended the first-half scoring. In the third minute after the restart, winger Leicester Fainga'anuku finished a long-distance try from a wayward Blues' kick but the next 37 minutes were scoreless.
"There was plenty of defence out there tonight and some sore bodies," Barrett said.
"They just took their opportunities. There weren't many in that game.
"When we sped the ball up in the second half we started to see some opportunities through the middle but we weren't good enough to execute and finish."