The Mariners looked primed to walk away with the three points at Industree Group Stadium on Friday after Isabel Gomez opened the scoring in the 68th minute.
But the Wanderers rallied, with Olivia Price equalising in the 80th before Caspers found the back of the net three minutes into added time.
A pass from Central Coast goalkeeper Sarah Langford to defender Jess Nash fell short, allowing Caspers to pounce.
Western Sydney are ninth ahead of the weekend's matches after securing their third-straight win, sitting nine points out of top six with six rounds remaining.
It is a hammer blow for the sixth-placed Mariners, who extend their losing run to two games.
A suspected left leg injury to Gomez only adds to their woe, the Matildas hopeful going down in the 85th minute after a contest with Caspers.
Gomez had suffered a right knee injury in November just days after earning her first national team call-up for friendlies against Brazil and Taiwan.
Wanderers keeper Shan Khamis held her nerve to keep Central Coast at bay in the first half.
Annalise Rasmussen led the way with two brilliant shots down the right wing, forcing brilliant saves from Khamis in the ninth and 12th minute.
Peta Trimis tried her luck in the 10th minute after Brooke Nunn threaded the ball through the Wanderers defence, but Khamis dived before she could attempt a shot.
Khamis was again tested when Gomez danced around a number of Wanderers defenders to try her luck at goal.
At the other end, Western Sydney captain Amy Harrison produced two quality through balls to spark an attack.
Harrison first set up winger Price, who gave up the ball to Annabel Martin.
Bronte Trew was on the receiving end of another Harrison pass after Central Coast's Taylor Ray failed to intercept, but Trew tried to cut back to a teammate instead of releasing the trigger herself.
Danika Matos had the best shot in the 35th minute when she outmanoeuvred Nash in the box, but instead sent the ball across the face of goal.
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