A fresh-faced Pompey side were knocked out of the Johnstone’s Paint Trophy in the first round at Exeter.
The Blues looked bright before the break, with Adam McGurk and Conor Chaplin both coming close to firing them ahead.
But Ryan Harley opened the scoring for Exeter from the penalty spot after the interval before Alex Nicholls secured their safe passage into the next stage.
Paul Cook handed debuts to three players as he selected a youthful side with only three players aged over 20.
One of those was fit-again summer signing Adam Barton, although the midfielder was handed a role in the centre of defence.
Academy starlets Calvin Davies and Brandon Joseph-Buadi also made their senior bows, while there were maiden starts for both Adam May and Ben Tollitt.
But the inexperienced outfit were unfazed and should have broken the deadlock after just 14 seconds.
A defensive error sent McGurk one-on-one with Bobby Olejnik, but the Grecians keeper got down quickly to parry the ball clear.
Pompey played with plenty of freedom in the opening stages, with Davies looking particularly keen to get forward down the right.
The hosts unsurprisingly started to see more of the ball as the half progressed, but Barton brought one dangerous move to an end, while Danny Butterfield then fired wildly over the bar.
David Wheeler did have the ball in the back of the net on 18 minutes, although referee Lee Swabey had long since blown his whistle for a shove on Adam Webster.
Alex Nicholls came closest to breaking the deadlock for Exeter with a swerving cross that a back-pedalling Paul Jones just about managed to prevent from dipping into the net.
Pompey were creating chances of their own, however, and Chaplin forced another decent stop from Olejnik after latching onto May’s threaded pass.
Tollitt then fired over when well-placed to test Olejnik before Craig Woodman made a vital clearance to stop Chaplin converting McGurk’s cross.
Then, with the interval approaching, Davies won a free-kick wide on the right and Chaplin stepped up to curl the ball against the bar.
Exeter City 0
It was the hosts who were first to threaten when Manny Oyeleke sent in a low cross that Ryan Harley turned narrowly wide.
But the Blues soon started to settle and there were half-chances for Tollitt and McGurk to trouble Exeter.
It was the Grecians who broke the deadlock on 54 minutes, however, after Joseph-Buadi brought down Tom McCready in the box.
Referee Lee Swabey pointed straight to the spot and Harley stepped up to emphatically slam home the penalty.
Cook soon made his first switch, with Kal Naismith becoming the latest debutant in place of Joseph-Buadi.
Chances were proving much more difficult to come by in the second half, although skipper Ben Close did have a long-range drive blocked.
But Exeter doubled their advantage on 72 minutes when Nicholls’ shot from out wide flew past Jones’ grasp and into the net.
Another youngster was then handed his senior bow as Christian Oxlade-Chamberlain replaced McGurk.
And Brandon Haunstrup made way on 82 minutes as Kaleem Haitham became the next player off the production line.
The young guns were unable to inspire an unlikely comeback, but the travelling fans still seemed pleased with their glimpse of what the future might hold for Pompey.
Exeter (4-3-3): Olejnik; McCready, Tillson (c), Moore-Taylor, Woodman; Oyeleke, Butterfield, Harley (Jay 60); Nicholls, Wheeler (Morrison 60), Holmes (Reid 75)
Goals: Harley 54 (pen), Nicholls 72
Subs not used: Hamon, Brown
Pompey (4-2-3-1): Jones; C.Davies, Webster, Barton, Haunstrup (Haitham 82); May, Close (c); Tollitt, Chaplin, Joseph-Buadi (Naismith 66); McGurk (Oxlade-Chamberlain 77)
Subs not used: Bass, Yates
Referee: Lee Swabey
Attendance: 2,323 (515 Pompey fans)