Both sides went into the game with underwhelming starts to the season, seeing them in the bottom half of the table, cut Barnsley turned their fortunes around with goals from Ike Ugbo and Harvey Barnes in the first half and George Moncur in the second.
And Heckingbottom said: “I’m very happy and I’m pleased for the players because they’ve deserved it. I think it’s been coming, to be honest. It gives them confidence.
“We have to play to our strengths and try and hide our weaknesses and I think we did that today.”
On selecting youngster Ugbo over regular striker Tom Bradshaw, Heckingbottom said: “I was pleased with him. We had a training game and he scored four the other day.
“He showed his qualities today and his challenge is doing that in the Championship this season.
“The most pleasing thing about the win was the storm we weathered at the beginning. A lot of it was our own doing and things we were getting wrong.
“But we defended our box really well, made blocks and tackles when we had to and didn’t panic, which was the main thing.”
Sunderland started brightly but it was Barnsley who took the lead in the 31st minute with summer signing Ugbo bundling the ball home following a save from Sunderland keeper Robbin Ruiter.
Barnsley quickly added to their advantage with Barnes’ spectacular volley from inside the box making it 2-0 in the 35th minute, following a poor defensive clearance from a below-par Lamine Kone.
Sunderland will feel aggrieved, however, with referee Chris Kavanagh, who gave Liam Lindsey only a yellow card for a foul on James Vaughan who was through on goal.
Sunderland put in a miserable display and were second best to everything. Barnsley finally got what their performance deserved in the 67th minute when Moncur, who was put through by Ugbo, brilliantly smashed the ball into the top corner to finish off the north-east side.
On his side’s poor performance, Sunderland boss Simon Grayson said: “They deserved to win the game because they did the basics right. They ran further and harder, they made tackles and that’s what the Championship is about.
“It’s never acceptable to lose a game and it’s certainly not acceptable to lose a game in the manner that we did.
“Too many players wanted to do their own individual stuff instead of playing for the shape of the team. They didn’t work hard for each other and Barnsley found it quite easy to score the first goal.
“Our fans had a go and rightly so. When they’re seeing players not doing what’s required and earning money to play for the shirt they can voice their opinions. I’ve got no problem with that.”