West Coast have staged a stunning second-half comeback to score a vital eight-point AFL win over St Kilda at Telstra Dome.

Young Eagles midfielder Matt Priddis starred as his side won 16.10 (106) to 14.14 (98), putting the finals hopes of the eighth-placed Saints in jeopardy.

St Kilda are half a game ahead of Brisbane and Adelaide, who clash on Saturday night at AAMI Stadium in another crucial round-21 match.

Saints ruckman Justin Koschitzke goaled with 21 seconds left to reduce the margin to two points, but Priddis was again prominent at the next centre bounce and West Coast won the clearance through Ben Cousins.

Mark LeCras then goaled on the run to seal the game.

The third-placed Eagles will start strong favourites next week at home against Essendon and they should seal a top-four finish.

They are level on points with second-placed Port Adelaide and only just behind the Power on percentage, meaning a home final is well within reach.

In his 23rd senior game, 22-year-old Priddis showed he is heading for elite status in the richly-talented West Coast midfield.

He led the way with 36 touches as the Eagles rallied from 22 points behind at half-time, while key forward Quinten Lynch kicked five goals and full-back Darren Glass blanketed Fraser Gehrig.

On Thursday, assistant coach Peter Sumich nominated Priddis as one of the keys if the Eagles were to cope with their personnel problems.

Eagles star Daniel Kerr needed finger surgery this week and he is unlikely to return unless they make the grand final.

Other front-line players such as Norm Smith Medallist Andrew Embley and Daniel Chick are also injured.

Captain Chris Judd returned from a week off, but was restricted to the forward line and spent much of the frenetic last term on the bench as he clearly continues to struggle with a groin problem.

Cousins also returned from hamstring soreness and improved noticeably as the game progressed.

Eagles key forward Ashley Hansen appeared to suffer a hamstring injury during the final term.

Priddis was awesome during the third term as the Eagles kicked five goals to one, turning a 22-point deficit at half-time to a one-goal lead at the final change.

They kicked the first two goals at the start of the last quarter to lead by 17 points, before the Saints rallied with five of the last seven goals in the match.

It was a massive turnaround from the first half, when the Saints frequently looked set to blow the Eagles away.

Centre half-forward Nick Riewoldt and onballer Lenny Hayes led the way as St Kilda opened strongly and led by 28 points at quarter-time.

West Coast rallied with the opening three goals of the second quarter to trail by only eight points.

But just when they had regained touch, the Saints kicked three themselves to resume control.

Eagles ruckman Mark Seaby missed a crucial set shot after the siren and West Coast kicked another four behinds to open the second half.

Led by Priddis, the Eagles steadily worked their way back into the match and within minutes, it was the Saints who were in trouble.

Adding to a bad night for the Saints, utility Jayden Attard went down in the third term with a potentially serious knee injury.

Attard needed help from two trainers to leave the field and coach Ross Lyon said it could be an anterior cruciate ligament injury.

The Saints will know more when Attard's knee is assessed.

"It looks reasonably significant, but further investigations tomorrow," Lyon said.

While St Kilda will start favourites next Saturday against bottom side Richmond at the MCG, they will now need other results to fall their way to make the finals.

Lyon bemoaned the Saints' overuse of the ball in the third term, which he said invited West Coast back into the game.

"I can't question my boys' effort and hardness ... our skill level and over-finesse was really costly in the washup, that's the lesson," he said.

"It leaves us with a game to win and Richmond are playing really good football at the minute.

"The results can fall a way that enable us to play finals, if we were to win next week.

"Clearly, Brisbane and Adelaide are the key to that."

Eagles coach John Worsfold praised his team for being able to regroup quickly after a poor start, make several changes and eventually overhaul the Saints in a high-quality game.

"The only benefit about having a bad first quarter is that there's three quarters to go," Worsfold said.

"I was really pleased with the players to be able to adapt to a few changes we made during the game, we changed their roles and the way we wanted to move the ball.

"(We had) turnover issues early - that was probably the key worry ... really bad mistakes."

Worsfold heaped praise on Priddis, saying he had met the challenge well.

"Competing against some quality players in St Kilda's midfield, he has to step up and take on some of the bigger-name players," Worsfold said.

"He certainly won't be the third or fourth midfielder for us that might sneak out there ... he's a quality player and prepares to get the best out of himself.

"To play like he did tonight is outstanding."

Worsfold said Judd did not need a fitness test earlier but said he would probably not play next week in the lead-up to the finals.

"The good thing is he felt good enough to play, there's every likelihood we won't play him next week," Worsfold said.

"We'll be confident he'll come up the week after.

"When he came off during the last quarter I just asked how he was feeling and he said he's okay."

Worsfold added the Eagles were uncertain if Hansen suffered a hamstring strain or only cramp.

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