West Coast survived a frenetic Carlton fightback to post a thrilling three-point AFL semi-final victory at a packed Patersons Stadium on Saturday night.

The Eagles looked to have the game in the bag when Mark LeCras kicked truly to give the home side a 21-point lead at the 22-minute mark of the final term.

But the game was turned on its head when Carlton booted three goals within eight minutes to close within a kick.

Substitute Zach Tuohy had the chance to win it when he launched a scrambled snap in the dying moments, but Eagles defender Sam Butler punched the ball through for a behind to secure the 15.11 (101) to 15.8 (98) triumph.

West Coast's first finals win since their premiership year of 2006 set up a dream preliminary final clash with Geelong at the MCG next Saturday, while Carlton's season of promise is over.

However, Blues coach Brett Ratten is almost certain to have his contract extended after guiding his charges to fifth spot and an elimination final win over Essendon.

West Coast coach John Worsfold will also be given a new deal at season's end.

Remarkably, he is just one win away from guiding his team from the wooden spoon to the grand final within the space of 12 months.

Carlton skipper Chris Judd failed to fire for the second straight final, managing just 17 possessions against Scott Selwood a week after being held to 19 disposals by Essendon's Heath Hocking.

West Coast were well served by ruckman Dean Cox and midfielder Daniel Kerr, while Mark Nicoski, Jack Darling and Josh Kennedy booted three goals apiece.

The Eagles looked far from assured of a preliminary final berth when Carlton shot out of the blocks with the opening four goals of the match inside 17 minutes.

However, West Coast hit back in grand style in the second term, booting eight goals to three to set up the victory.

Kennedy's night appeared over in the first term after a heavy head clash with Carlton's Lachie Henderson left him feeling physically ill.

But the 24-year-old returned to the fray in memorable fashion in the second quarter, booting a remarkable 65m goal that took a Shane Warne-style leg break before evading an outstretched Dennis Armfield near the goalline.

Carlton suffered a major blow on the stroke of halftime when utility Bret Thornton knocked himself out after flying high for a mark and landing heavily, forcing the Blues to activate Tuohy.

Thornton was taken to hospital to determine the severity of the head injury - the second time he has been forced to visit a Perth hospital this year after copping a heavy knock to the face in Carlton's win over Fremantle in round 21.

The third quarter was a pulsating affair as the pressure lifted a notch and players threw themselves at the contest.

But it was nothing compared to the final term, with Carlton falling only just short in a brave effort on enemy territory.

Carlton coach Brett Ratten praised the efforts of his troops.

"I couldn't really ask too much more out of the players," Ratten said.

"I thought they gave everything they had.

"Even with Thornton going off, his effort to contest in that situation - sometimes it comes at a cost.

"Their effort across the board was very good."

With the last quarter lasting almost 36 minutes, West Coast coach John Worsfold admitted it was a nervous time in the coaching box.

"It was a long, long last quarter," Worsfold said.

"We have a countdown clock.

"We tried not to look at it too early in the quarter ... because 27 minutes takes a long time to count down if I start looking at it then."

Worsfold said Kennedy, who had swelling around his left eye, would undergo precautionary scans to determine if he had suffered a facial fracture.

Carlton forward Andrew Walker, who booted three goals, had a chance to mark Tuohy's late snap, but was brought to ground as he and Darren Glass wrestled for best position.

When asked whether he thought Walker was stiff not to get a free kick, Ratten replied: "You probably said the words. I don't even have to say it.

"Anyway ... it's a game of inches. I won't even comment any further."

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