The Argentinian pounced to steer home a rebound after Ryan Shotton's towering header from Iain Hume's 77th-minute corner had been brilliantly saved by visiting goalkeeper Chris Weale.
Barnsley's recent steady climb towards the top half of the table had faltered in recent weeks after successive league defeats to Coventry and Sheffield Wednesday, but De Silva remains upbeat.
He told the club's official website: "We have a lot of confidence in the dressing room and winning matches can only increase that. Every game is different and we have to take care to understand each other.
"It is important now to keep those levels of performance and concentration up in each and every match. We know that if we can do that and play to our maximum level that we can make a move up the table."