The Irish international set up Sibieski to conclude the scoring in the 3-1 win over Aston Villa, and the delight on his face said it all. Glenn Roeder knows his problem and has told the winger to stop punishing himself.
Will Goal Transform Duff's Form?
The 27-year-old put in only his second appearance in 15 games since undergoing surgery to repair cartilage.
Roeder: "Damien Duff is self-critical - he is too self-critical at times. You can be too analytical and put unnecessary pressure on yourself.
"But at least that shows you how much he cares and how much he wants to do well for Newcastle.
"Even for him, settling in probably has not been easy. He has moved from one end of the country to the other, he has come from the team that has just won the Premiership twice and cultures will be different.
"Just because he is an experienced player does not mean he is going to settle in straight away and find his best form.
"I have a feeling - and I hope I am right - that although we did not want him to have this enforced break through injury, maybe that is just what he needed to finally settle in, come back fresh and play a big part in us establishing ourselves in the top half of the table between now and the end of the season.
"I am very positive in the remainder of this season that we will see the Damien Duff that he expects of himself."