Burley's men thought they had weathered a late storm from Wednesday but the 37-year-old veteran, on loan from Fulham, headed an injury-time equaliser to send the home fans wild.
Burley's expensively assembled South Coast side looked set to keep up their impressive run and move into third spot thanks to goals from Grzegorz Rasiak, Kenwyne Jones and Bradley Wright-Phillips.
But Wednesday hit back with two goals from Glenn Whelan followed by Crossley's stunner which silenced the visiting fans.
Despite a high-energy start from Wednesday, Saints went ahead when £7million-rated Gareth Bale broke down the left and fed a smart ball for Rasiak, who slipped his marker and placed a super shot over Crossley to claim his 15th goal of the season.
Ten minutes later the Saints were showing their class again when Bale whipped in a free-kick but Jones powered his header over the top.
In the 25th minute the visitors stretched their lead after a hotly-disputed corner. Jermaine Wright crossed the ball into the six-yard box and Jones produced a towering header from close range.
The two-goal advantage lasted just a minute before Wednesday pulled one back. Whelan collected the ball in space midway inside the Saints half and cleverly went round Bale, cut inside and cracked his low shot past Kelvin Davis.
Wednesday continued to search for the equaliser and forced back the visitors with Chris Brunt driving a low shot that Davis hung onto and Frankie Simek volleying just wide after Marcus Tudgay had flicked up the ball for him.
The second goal came after 69 minutes when Simek's throw-in was headed out and Whelan volleyed a splendid goal from the edge of the area.
Five minutes later Madjid Bougherra deserved a leveller for his overhead kick that was denied by a fine save from Davis.
And in the dying minutes Wednesday hurled everything forward forcing Saints back. With the last throw of the dice Crossley galloped forward, urged on by the home fans deep into three minutes of injury time, and duly headed in Brunt's corner.