The Blues' Super 14 rugby season hung by a thin thread after they lost 26-22 to the Crusaders in Christchurch.

Despite earning a bonus point for finishing within seven points, the Blues' playoff chances now depend on them winning their remaining three games as well as other results favouring them.

Hooker Corey Flynn scored two of the Crusaders' four tries as the home side rebounded from last weekend's first loss of the season to the Chiefs.

The Blues hammered the Crusaders line in the last 11 minutes as captain Troy Flavell and centre Anthony Tuitavake appeared to scores tries only for television replays to show they were either in touch before touching down or held up.

They were finally rewarded for their determination when winger David Smith scored their third try in the 74th minute.

But the Crusaders held on to improve their place atop the standings to 43 points.

The Sharks, who meet the Waratahs in Sydney on Saturday, are second with 32 points.

The Crusaders led 12-0 following tries by captain Richie McCaw and Flynn and looked like taking the Blues apart with a clinical game.

But basic errors crept into both sides' game as the battle intensified and referee Lyndon Bray began to feature as passes were dropped, the ball was knocked on and the rucks became messy.

Flynn, after scoring his two tries, was sin-binned for a dangerous tackle in the 64th minute.

The Blues saw their chances with a man short in the opposition but continually muffed them by taking some difficult options in attack.

It was then that the Crusaders tightened their play, recycled the ball more efficiently and scored their bonus point-earning fourth try through replacement hooker Ti'i Paulo.

"It got pretty frantic in the end but (I'm) quite happy to come on the right side of it," McCaw said.

"I think we finished the opportunities we got and that's the key to games like this, especially against the Blues. We had to dig pretty deep when we were a man down."

Flavell said he was disappointed the Blues did not take advantage of their opportunities.

"We've got to keep our confidence up. If we keep the same sort of attitude we had in the game out there we could knock the next three teams over," he said.

Blues openside flanker Daniel Braid was penalised for a third time in the 11th minute, allowing the Crusaders to opt for an ideal attacking scrum 30m in front of the posts, and McCaw was sent over by Leon MacDonald.

Stephen Brett converted and the Crusaders led 7-0.

Next in for a try was Flynn in the 26th minute when blindside flanker Kieran Read engaged two defenders to clear the way after a ruck 40m away.

The Blues' response was almost immediate.

Read's opposite number, Jerome Kaino, smashed through two tacklers, including Flynn, to enable winger Rudi Wulf through.

When No.8 Nick Williams rammed his way over and Nick Evans converted, the Blues led 14-12.

The Crusaders regained the advantage only two minutes later when they broke away from inside their own 22 with superb support play and Flynn finished it to complete his double.

Brett missed two penalties before Evans closed the gap to 19-17 but, when nothing seemed on, Crusaders left winger Sean Maitland latched on to a kick ahead by centre Tim Bateman and miraculously avoided the touchline to let Paulo through for their fourth try.

The Blues responded with Smith's try but ran out of time.

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