Darius Henderson came off the bench to head home an 85th-minute winner for the Reds on a day when manager Davies sat out a one-match touchline ban, following his angry confrontation with referee Craig Pawson at Wigan before the international break.
But deputy manager David Kelly said it was a carefully orchestrated game plan from the Reds, who saw Djamel Abdoun, Jamie Paterson and Henderson all impress after coming off the bench.
"The substitutions were very productive, they worked really well - the gaffer is really big on making impact substitutions," said Kelly, who had seen his side take the lead twice through Simon Cox and a Kelvin Etuhu own goal.
Barnsley levelled twice, however, firstly through a Chris O'Grady penalty and then with a spectacular free kick from Tomasz Cywka.
"They did very well when they came on - helping us to win a game we deserved to win," Kelly added.
"I have spoken to the gaffer and he (Davies) is pleased, obviously very pleased. There are difficult games in the Championship, games where teams will come and park the bus a little bit.
"We were patient and we have a never-say-die attitude. The players have a desire and a will to win.
"We thoroughly deserve the three points - we hit the post three times, we had numerous one-on-one opportunities with the keeper and, at one stage in the first half, I felt we could have been 4-1 up - that was probably after about 20 minutes!"
Barnsley boss David Flitcroft felt his side were unlucky not to collect their first away point of the season.
"It was an open encounter and I was happy with how my team tried to create chances. But I am disappointed that we did not take a point," he said.
"We did not deserve to win the game, they had a lot of good chances and (goalkeeper) Mike Pollitt was in excellent form.
"But the penalty was deserved and, if you see a better goal than the one from Cywka today, I would be surprised.
"I wanted the lads to dig in for one more moment. But they didn't. We have not got anything from today, but I am happy that we only have a few days until we play again (at Bournemouth)."