Man-of-the-match Duke pulled off half a dozen top-class saves to defy Aston Villa, while Nahki Wells' clinical first-half finish and two thumping headers late in the second period from defenders Rory McArdle and Carl McHugh, either side of Villa striker Andreas Weimann's 82nd-minute effort, clinched npower League Two heroes Bradford a 3-1 Capital One Cup semi-final first leg victory.
Wigan had been sent packing in round four and Arsenal famously despatched in the quarter-finals as another extraordinary night of giant-killing football unfolded in West Yorkshire, but 6ft 5in Duke remained unmoved. Promotion remained the Bantams' main objective this season.
The Sheffield-born keeper, who had obviously listened carefully to boss Parkinson's post-match gambit, said: "It was a fantastic performance. We gave them a game, but we are only halfway there.
"We have got to go and do it again and even better. We cannot get carried away. We have got some important league games coming up. These are our bread and butter and we want to get out of League Two."
Duke, 35, is in his second season at Bradford - he doubles up as goalkeeping coach - having joined them just after Parkinson took charge at Valley Parade in August 2011.
Duke, who played for his current boss during their time together at Hull, was out of contract at the KC Stadium when Parkinson signed him within days of replacing former Bradford boss Peter Jackson
"Things didn't work out as I wanted last season, but I'm beginning to show what I'm capable of now," Duke said.
He brilliantly thwarted Christian Benteke twice, Charles N'Zogbia and Gabriel Agbonlahor in the first half and maintained impressive concentration levels to keep out Benteke's diving header and another goalbound Agbonlahor effort after the break.
"For me, it was one of those nights - the shots were coming in," the former Burton number one said.
"I've played a lot of games at different standards and I'm just thankful I could make those saves, but give credit to the lads in front of me - they were fantastic.
"You see how they performed - it gives you confidence."
A crowd of 22,245, swelled by Villa's 4,313 travelling fans, were treated to another memorable night at Valley Parade.
"We've got a good bunch of lads and team spirit takes you a long way," Duke added.
"It's great to give the crowd something to shout about.
"We would have snatched a hand off if we had been offered 3-1, but there will be big pressure on us at Villa Park.
"They will be at us straight away, it's going to be a massive game, but to get that third goal was massive and it gave us a two-goal cushion."
Parkinson, whose contract expires at the end of the season, hopes to open talks with City's joint chairmen Julian Rhodes and Mark Lawn this week.
The 45-year-old was also mindful not to get carried away, saying: "It was important we got the message across to the lads at the end of the game and equally be respectful to Villa because in two weeks' time we've got to go down to Villa Park and do it all again.
"We're absolutely delighted with the way we played, obviously, because from the first minute to the last the lads were tremendous. But equally we know we're only halfway there, we've got a very difficult job in a fortnight's time."