It could well have been Phunya Sele Sele who emerged victorious from a see-saw game, but a succession of missed chances by the visitors late in the match proved costly as the Buccaneers rode their luck somewhat before joining SuperSport United, Chippa United and Golden Arrows in the semis.
Despite an energetic start to the game by Pirates, in particular, there were hardly any chances on goal in the opening 30 minutes.
It was Celtic who did manage to get in a couple of efforts, but Lantshene Phalane’s long range effort went straight down the throat of Siyabonga Mpontshane while Musa Nyatama’s well-hit curler from 25-yards flew inches wide of goal before Wandisile Letlabika and Phalane again shot over the bar.
Status quo was resumed after the interval as Deon Hotto sent a 25-yard effort over the bar before Lyle Lakay cut in from the left and fired into the side-netting.
But it was the Sea Robbers who were to score with virtually their first visit to the Celtic box when Abbubaker Mobara fired in clinically from a tight angle on 53 minutes after an Issa Sarr through ball.
Lakay could have restored parity within a minute but failed to score after Thabo Matlaba got back to clear off the line.
The atmosphere remained tense and Mpho Makola and Gabuza missed chances to give the Buccaneers the cushion of a second goal.
Bucs seemed to be edging towards victory only for Kabelo Mahlasela to grab the equaliser just four minutes from the end of regulation time when he squeezed a low shot into the bottom corner after being given space on the edge of the box.
Lakay and Mahlasela both had chances to win the game for Celtic, but the former shot narrowly wide and the latter was foiled by Mpontshane.
The Free State side had more opportunities to go ahead in extra time, but Ayanda Dlamini and Lakay both missed out.
It was left to Gabuza to wrap up a victory for Pirates when he sent a thumping header into the bottom corner after Thabo Rakhale’s excellent cross.
The Free State side spurned a wonderful chance to draw level again when Mahlasela fired over from right in front of goal five minutes from time as the Soweto side held on anxiously for victory.