Andre Ayew's solitary first-half strike at Oakwell has given Swansea a slender 1-0 lead in their Sky Bet Championship play-off semi-final against Barnsley.
Ayew produced the game's only moment of class six minutes before half-time in the first leg when he curled home a crucial goal for Steve Cooper's side.
Swansea, who will defend their narrow advantage on Saturday in the return leg at the Liberty Stadium, owed much to goalkeeper Freddie Woodman's brilliant second-half save, while the Yorkshire club also struck the crossbar late on.
Around 4,500 Reds fans were allowed back in to watch their side for the first time since March 2020.
It was the first time Barnsley head coach Valerien Ismael, appointed in October last year, had walked to his dugout in front of a crowd and he received a rapturous reception.
The 45-year-old has transformed Barnsley from relegation candidates to Premier League hopefuls in seven months, while Swansea have reached the play-offs for the second-consecutive season.
The home side were first to threaten when fit-again skipper Alex Mowatt's effort curled off target.
It was fast and furious, but low on finesse and the first moment of quality provided Swansea with the breakthrough in the 39th minute.
Ayew received Kyle Naughton's pass down the right channel and his sharp turn inside gave him space to curl a sweet left-footed finish inside the far post for his 18th goal of the season.
Barnsley responded, but defender Michal Helik's header lacked power and was easily gathered by Swansea goalkeeper Woodman.
Reds forward Carlton Morris replaced Dominik Frieser at half-time and had an instant impact as his shot was saved by Woodman, who then superbly denied Callum Brittain on the rebound.
Mowatt's free-kick was saved by Woodman as Swansea were swept on to the back foot, but the visitors weathered the storm.
Republic of Ireland international Conor Hourihane, a former Barnsley captain who is has been on loan at Swansea this season, saw his free-kick tipped away by Brad Collins and Jamal Lowe curled an effort just off target.
The visitors did all they could to slow the game down and their time-wasting tactics became more pronounced. With 10 minutes left it was all going to the Welsh side's plan.
That was almost undone in the closing moments when Carlton Morris turned the ball goalwards from Mowatt's corner, only to see his curling effort hit the crossbar.
Swansea survived and extended their unbeaten run against Barnsley to 17 matches.
The Reds beat the Welsh club on penalties in the League One play-off final in 2006, but their last victory against them over 90 minutes was back in 1983.