The try was worth the admission price alone - a sumptuous wrap-around between Sexton and Berne set D'Arcy free near halfway and his well-placed pass put Nacewa thundering past Fussell and over from 30 metres out.
Berne tagged on a drop goal soon after and Leinster's lead was out to 17-6.
Credit to the Dragons, they maintained their composure and hit back when Tom Riley tied up D'Arcy near the Leinster 22, allowing Fussell the time and space to put full-back Thomas through for an unconverted try.
Sexton steadied the home ship with a close range penalty but the Leinster out-half saw yellow for a ruck offence and Arlidge kicked the Dragons to a likely bonus point.
However, Leinster pressed on and Berne's final-minute drop goal confirmed the Irish province's tenth successive win at the RDS.
Speaking after the game, a pleased Sean O'Brien said: "It was a very important result. We had to bounce back after last week's defeat to the Scarlets and it was a good win, so we're happy.
"With so much competition in the pack I'm not that fussed where I play. So long as I play!
"We stepped it up a gear (after the replacements came in) and we're trying to build all the time. So we're happy, but we know that we have areas to improve."
|Leinster Rugby Score Card|
|Newport Gwent Dragons Score Card|