Hales made 63 from 42 balls and Duckett 64 from 40 as they added 92 in nine overs to lift the Outlaws to 198 for 5 after the Falcons had put them in.
Luis Reece scored 61 from 42 balls but Gurney bowled superbly to claim 5 for 30, his best T20 figures, as the Falcons could only manage 171 for 8.
The Outlaws had made a measured start with Hales and Joe Clarke selecting placement over power until Clarke skied a big drive at Fynn Hudson- Prentice in the sixth over.
Duckett drove Matt Critchley for the first six in the ninth over as the Outlaws engaged the turbo with Hales driving Alex Hughes onto the media centre balcony and lifting Mark Watt for another maximum.
The Falcons lost Logan van Beek with a shoulder injury before Duckett survived a swirling catch to cover on 32 off Watt who kicked the air in frustration when Hales drove him straight for his third six.
Duckett pulled Critchley over the midwicket boundary but the leg-spinner broke the stand in the 15th over when Hales was caught at wide long-on and Dan Cristian became his second victim when he sliced a drive to mid off.
Tom Moores was bowled behind his legs by Ravi Rampaul and Ducket was brilliantly caught on the cover boundary but Samit Patel struck 14 from five balls to set a challenging target.
Hudson-Prentice took two fours from Matt Carter’s opening over and Billy Godleman pulled Gurney for six but the seamer responded by having Hudson-Prentice caught at cover off a sliced drive.
Reece drove Carter over long off and pulled Jake Ball for another six to take the Falcons to 53 for 1 at the end of the powerplay.
Godleman was reprieved on 19 when Ben Duckett just failed to take a diving one-handed catch at cover, injuring himself in the process, and the Outlaws turned the screw to leave the Falcons needing 115 off the last 10 overs.
The climbing run-rate forced Godleman to pull Gurney to deep square leg and although Reece drove Patel for his third six to reach 50 off 29 balls, Wayne Madsen became Imad Wasim’s first victim for the Outlaws in the 14th over.
Reece and Leus du Plooy took 14 from a Carter over but Reece was caught behind trying to scoop Gurney who settled it by removing Critchley and du Plooy in his final over as the game finished in pouring rain.
Nottinghamshire’s Harry Gurney said: “With the rain coming down I thought it was the right decision to stay out there and finish it.
“They got off to a decent start and we knew we had to bowl well through the middle and I thought as a group we did that and put pressure on them. We kept taking wickets and with Duckworth/Lewis creeping up it just piles the pressure on the opposition.
“That’s two in a row now so hopefully we can build some momentum now and if we can win tomorrow against the Leicestershire Foxes we can have a few days off with three wins on the board.”
Derbyshire captain Billy Godleman said: “I thought we would have been more comfortable restricting them to around 180. Alex (Hales ) and Ben (Duckett) played really well and with those two making a contribution that was the reason they got closer to 200 than we did.
“I thought our best chance of winning the game was to restrict them to as little as possible and see how the wicket played and then be more clear about how we would then try and chase down their total.
“Reecey (Luis Reece) played excellently but for us to chase 200 you either need two contributions or for him to go on and reach three figures which is very difficult with the run rate increasing.”