Famously, he wondered in vastly different circumstances "Was this what it's all about." The same question will torture his now shattered dreams for days, weeks and months to come.
"No, I dreamed like everyone else," he muttered disconsolately. "I dreamed of going the whole way. Obviously it's not going to pan out. What can you say?
"Before the game we definitely believed that we could grind out a result. And I mean that genuinely."
While Simon Cox, who expressed his "disappointment" at being withdrawn prematurely, felt his side lacked combative strength up front, and Glen Whelan bemoaned the familiarly thin population in midfield as, for the second successive occasion, previously unheralded defensive frailties handicapped Ireland.
Any pre-match plans, formation tinkering or purported system strengths were undone by the team's Achilles heel all tournament - the concession of appallingly sloppy goals at the beginning of either half.
"We didn't help ourselves tonight," lamented Duff. In the course of a flash two-minute debrief, he repeated the sentiment on seven different occasions.
"I suppose you could say we gifted them three or four goals tonight. They're always going to create chances, they're the best international team in the world.
"Even at 1-0 at half-time, you're thinking if you can keep it at that for 20 or 25 minutes, maybe they'll get a bit of nervous.
"You're going to get pulled all over the place really with them. We did well at times, defended well at times. But we shot ourselves in the foot again."
Aiden McGeady, just as anonymous as Duff on the opposite wing, within a team who could not hope to provide them with any service, also lamented lapses.
"It is a team collectively and it is everyone to blame," said McGeady. "If we had kept it tighter at the back in the first 10 minutes and again in the second half it might have been different, but we couldn't get the ball off them."
The disappointment threatens to seep into Ireland's last encounter, an academic exercise, but one filled with meaning for the manager and the country's unbelievably loyal support.
"Going past the Spanish dressing-room, the music's playing," said Keith Andrews, Ireland's best performer. "It isn't exactly lively in our dressing-room. We're disappointed in ourselves."
COMMENT RULES: Comments that are judged to be defamatory, abusive or in bad taste are not acceptable and contributors who consistently fall below certain criteria will be permanently blacklisted. The moderator will not enter into debate with individual contributors and the moderator’s decision is final. It is Belfast Telegraph policy to close comments on court cases, tribunals and active legal investigations. We may also close comments on articles which are being targeted for abuse. Problems with commenting? email@example.com