It looked as though the sides were going to see out a goalless draw, as second-half substitute Sam Vokes struck the post in the 81st minute for Wycombe and saw a follow-up effort from Sadlier well blocked again by Grehan.
In the 89th minute, while turning his body to defend a cross inside the box, Grehan was adjudged to have handled the ball. Luke Leahy, Wycombe’s number 10, stepped up from the spot and Whitworth pulled off a fantastic stop to deny him.
Unfortunately, the Chairboys were handed a lifeline with an opportunity to retake the penalty, as the referee had deemed Whitworth to be off his line when he made the save. Leahy duly converted at the second time of asking in the 92nd minute, despite Whitworth diving the right way.
A sucker punch of a goal that really took the wind out of the Palace side in the six additional minutes that were played. Powell’s side will have to pick themselves up and dust themselves down with Nottingham Forest to come in the Premier League 2 next.
Wycombe: Ravizzoli (GK), Forino (Low, 62), Wheeler (Potts, 78), Breckin, Boyes (Leahy, 62), Keogh, Taylor (Vokes, 62), Sadlier (Clark, 86), de Baar, Pattenden, Skura.
Subs not used: Shala (GK), Woodhouse.
Palace: Whitworth (GK), Imray, Sheridan, Grehan, Watson, Raymond, Ozoh (Devenny, 45), Umeh, Ebiowei (Eze, 73), Mathurin (Mustapha, 58), Akinwale (Francis, 85).
Subs not used: Izquierdo (GK), Cardines, Dashi.