The Crusaders all-but sealed a home semi-final by beating the Sharks 18-10 in a Super 14 rugby match in rainy Christchurch.

The win kept them on top of the table on 47 points and only nearest rivals, the Waratahs, have a realistic chance of taking the minor premiership from them.

The loss plunged the Sharks deeper into a dogfight for a semi-final place, as they emerged without a point and remained in a tie for third with the Chiefs.

The Crusaders did a huge favour for New Zealand sides the Chiefs and Hurricanes, who are in hot pursuit of a top four finish, with South Africa's Stormers also contenders.

For the Sharks, unbeaten after eight matches, it was their third loss in a row after going down to the Brumbies and NSW in Australia.

In the process, the Sharks continued their record of never having won in Christchurch and Sharks skipper Johann Muller said the home side's defence proved the difference.

"Their defence was unbelievable in the last 10 minutes of the second half," he said.

"We wanted to put them under pressure in the second half which we did, but we just couldn't turn that into points."

Props Greg Somerville and Wyatt Crockett, who replaced Ben Franks, scored the Crusaders' tries.

No.8 Ryan Kankowski replied for the Sharks in a fiercely-contested battle on a rainy night.

The Crusaders took an early lead with a Stephen Brett penalty and were rewarded with a try in the 18th minute after sustained pressure at the Sharks' line.

Brett added the points for a 10-0 lead which the Sharks could not close after missing a couple of easy penalties by five-eighth Ruan Pienaar and halfback Rory Kockott.

A mistake by Brett, kicking the ball out on the full at a 22 re-start, gave the Sharks a golden opportunity which Kankowski took brilliantly.

Off the back of the resultant scrum, Kankowski batted away weak tackles by Richie McCaw, Brett, Casey Laulala and Leon MacDonald as he surged for the line for a try which Kockott converted.

The teams exchanged penalties for a 13-10 halftime scoreline but almost on the hooter, McCaw was sinbinned for a professional foul in front of the sticks.

However, the Sharks were unable to benefit from McCaw's absence in the second half.

With five minutes to go, the Crusaders launched a counter-attack that ended with Crockett getting the nod from the television official after winning the chase for a loose ball in the scoring zone.

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