Andre Ayew, with a moment of quality out of keeping with the game, scored the only goal which decided a very tight game at Oakwell Callum Brittain had a good second-half chance saved and Carlton Morris hit the crossbar with one of the final kicks of the match.
Eight months into the job of Barnsley manager, it was the first time Ismael had seen his side play in front of supporters at Oakwell and he was blown away by the reception, although he thought it took his players some time to readjust.
"I want to thank the fans for an amazing atmosphere, it was incredible," said the Frenchman.
"It was a big reward for everyone to finish the season with such an atmosphere.
"I think the first 20, 25 minutes we felt the atmosphere because we didn't play well. There were a lot of mistakes and a lot of emotion and I can understand this.
"For their goal, Ayew came back from an offside position and we didn't deal with it. You can't blame the centre-back, he did his job and stepped out quickly.
"The second half was much better, we put the emotion aside and just focused on our gameplan."
It has been an incredible 436 days since fans were last allowed into Oakwell.
Then, they were seven points adrift of safety at the bottom of the Championship with only nine matches to play when the country went into lockdown.
Gerhard Struber guided the team to safety with a dramatic final-day draw at Brentford but the start of this season was difficult too, Ismael inherited a team yet to win in 2020-21 when he took over in October.
The transformation since has been astonishing, finishing fifth in the Championship with only Norwich City winning more points in 2021.
That was reflected in the ovation the home fans gave their players at the end of the final Oakwell match of the season.
The second leg is at the Liberty Stadium on Saturday. The winners of the tie will face the winners of Bournemouth and Brentford at Wembley on May 29. The Cherries won their semi-final home leg 1-0.
"We have a lot of inspiration," said Ismael. "We have comeback quality and a strong mindset.
"Now it's all about preparing for the game.
"At the beginning everybody says it's a 50-50 situation but now it's a clear picture and we know what can happen.
"In the second leg anything can happen. It's 1-0.
"We have nothing to lose.
"If we fight like we did in the second half and start like that we have a good chance."
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