Australia caught well in the outfield to reduce the Windies to 45-6, Ellyse Perry (2-2) removing the unsafe Deandra Dottin for just six.
With the last ball of her second over she teamed with Sophie Molineux to have Shemaine Campbelle caught at square leg.
Knight, 27, who led her team to a comfortable eight-wicket win over India for a spot in the final, expects a "really good and tight" game against Australia.
She wasn't alone as the match swung at the end of Australia's innings when Rachael Haynes (25 not out from 15) helped take 17 off one Deandra Dottin over to forge a competitive total on a turning wicket.
England could soon have lost their third wicket in the form of top scorer Natalie Sciver (54 not out off 43 balls; 4X5) had Poonam Yadav not dropped her at midwicket off Anuja Patil when the right-hander was on two. The left-arm spinner is an attacking option who takes wickets at key moments, with her worldwide scalps so far including Deandra Dottin and Harmanpreet Kaur.
Eight wickets in hand, 17 balls remaining. West Indies' hopes of a home final to do an encore of Kolkata 2016 went up in flames less than halfway into their chase of 143 on a sluggish surface where taking pace off the ball was vital.
She ended the game with figures of 2-2 off two overs.
That Australia were able to take advantage of this debatable tactical call was down to Alyssa Healy's brilliance again.
What a star Alyssa Healy is. Everyone is different but I know we came into this with a lot of confidence, it as just one of those days when we didn't come off where the bat was concerned. Mithali who had been a consistent scorer for India in the tournament many felt would've certainly made a difference and thus keeping her on the bench was a weird decision.
On 27 in the eight over a thick outside edge nearly cost her, but it was too touch for the keeper to grab.
She hit 46 off 38.
Australia has won the tournament three times. And boy did she enjoy it. After that, it all went downhill rather quickly; West Indies paying the price for misreading the pitch and bowling first.
The West Indies hard nut is so erratic. "It goes beyond giving the youngsters a chance", she added. Taniya Bhatia, who opened in Raj's stead, scored 11 off 19 balls, and Patil, who kept her place despite Raj recovering from the knee injury that had kept her out of India's last group game, fell for a first-ball duck and delivered 3.1 wicketless and expensive overs of offspin.
She opened the batting and her shocking night continued, chopping an Ellyse Perry in swinger onto her stumped for just six runs.