Swansea boss Steve Cooper warned it was "only half-time" after his side took a slender 1-0 lead in their Sky Bet Championship play-off semi-final against Barnsley.
Andre Ayew's excellent curling finish six minutes before half-time proved decisive and was a rare moment of quality in a fast and furious first leg at Oakwell.
Fans returned to the stadium for the first time since March 2020 and a crowd of around 4,500 created a super-charged atmosphere.
"Andre came up with a bit of magic to give us a small margin, but it's only half-time," said Copper, whose side were beaten 4-1 on aggregate by Brentford in last season's play-off semi-finals.
"We've been here before 12 months ago and the final whistle in the next game is the most important one."
Swansea were indebted to goalkeeper Freddie Woodman – he kept his 23rd clean sheet of the season in all competitions – for their narrow advantage going into Saturday's return leg.
He produced a brilliant point-blank save to deny Callum Brittain on the rebound in the second half having kept out substitute Carlton Morris' shot.
Cooper said: "He did play well tonight. He did his job. I thought his positional play was good. But we've no time to think too much about it – it's time to look forward.
"It was a good effort from the boys. We knew the game would be a certain type and if we didn't match them, we could come unstuck.
"We did match them and we had bits of quality, the goal was the obvious one.
"We looked a threat. It was an emotional game and it was great to have supporters and I can't wait to get back to our place on Saturday."
Barnsley boss Valerien Ismael felt his players had been affected by the emotion of the occasion in the first half, but was upbeat about their chances on Saturday due to their display after the interval.
"The performance in the second half gives us a good feeling for the second leg. Everything can happen," the 45-year-old said.
"Two years ago Leeds won at Derby 1-0 and everyone thought Leeds would go through. (There is) big pressure on Swansea. We will fight like the second half (on Saturday)."
It was the first time Valerien, who was appointed head coach in October, had taken charge of a game for Barnsley in front of a crowd.
"It was an amazing atmosphere I have to say. It felt like 30,000," he said.
"I think that the first 20-25 minutes we felt the atmosphere in the players, we didn't play well in transition."
Ismael felt Ayew had been offside for his goal, adding: "You can't blame the centre-back, he did his job to step up quickly and then the linesman has to do his job.
"But we have comeback quality, we have a strong mindset, the mentality in the team is good. We need to score on Saturday, it's as simple as that."