Star WA batsman Shaun Marsh (knee sprain) was also injured in Friday's match at Melbourne's Junction Oval as WA triumphed by 18 runs, collecting their 15th domestic one-day title.
In a see-sawing game highlighted by Hilton Cartwright's astonishing and crucial outfield catch, WA made 9-225 from their 50 overs before NSW were dismissed for 207 in 46.3 overs.
Richardson top-scored with 44, leading WA's rearguard fightback after they had slumped to 6-89.
An over after bowling Baxter Holt for a duck, Richardson pulled up awkwardly in his delivery stride and had to leave the field injured with NSW on 6-117.
Richardson took five wickets in the second Ashes Test win at Adelaide Oval, but then went out of the side because of soreness and was left out of the Pakistan tour squad.
No.3 Moises Henriques had paced the NSW innings with 43 from 75 balls when he belted spinner D'Arcy Short to long on.
Cartwright was horizontal when he took an all-time classic diving catch, leaving NSW 8-204.
It proved the match-winning moment - Henriques and Ben Dwarshuis, who was unbeaten on 31, had put on 36 for the eighth wicket and NSW appeared to be heading to a win.
Adam Zampa and Tanveer Sangha were then dismissed for ducks to end the match.
WA paceman Andrew Tye, who was on a hat-trick, took 4-30 and was named man of the match, while Aaron Hardie snared 3-41.
Matthew Kelly and Jason Behrendorff put on 52, a WA record for the 10th wicket in one dayers, and that proved the difference.
Kelly made 27 not out and Behrendorff hit two sixes off Hayden Kerr in the last over of the innings for his unbeaten 24.
While WA's score was well short of par on a wicket that did not appear to be playing too many tricks, it proved enough to thwart NSW .
Marsh gave WA an injury scare at 2-70 when he turned back quickly after attempting a quick single.
He had a sharp pain in his left leg and dropped to the ground in pain.
Marsh needed medical attention for several minutes before resuming his innings.
But two runs later, Adam Zampa bowled him for 29, ending his 61-run stand with Cameron Bancroft.
Zampa bowled captain Ashton Turner with his next delivery for a duck and Cartwright survived the hat-trick ball.
Matthew Gilkes dropped a sitter off Kelly when he had only made two.
Gilkes then caught Richardson in the deep to give Daniel Sams his third wicket and it was given out, despite the fielder appearing to touch the boundary rope with his foot.
Sams snared 3-45 from 10 overs and Zampa took 3-40.
NSW beat WA in last year's final.
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