But Palace finally won it with Yohan Cabaye’s penalty five minutes from time and an even later effort from substitute Fraizer Campbell.
Before Cabaye’s spot kick, Al-Habsi looked to have done enough to keep the Premier League outfit at bay.
The man from Oman suffered FA Cup heartache three seasons ago when a shoulder injury kept him out of Wigan’s team that beat Manchester City in the final.
And he obviously wanted another crack at a winner’s medal. Cabaye, twice, and Mile Jedinak, were left wondering how he had kept their efforts out.
But when Royals defender Jake Cooper pulled back Yannick Bolasie, earning his second yellow card, Cabaye put Palace on the road to Wembley – although even then Al-Habsi got a hand to the spot-kick.