Pompey snuck into the second round of the Papa John’s Trophy after comfortably beating Crystal Palace’s under-21 side at Fratton Park.
Miguel Azeez, Gassan Ahadme and George Hirst all opened their accounts for the club – the latter in stoppage-time – in a performance that was full of attacking verve.
And with AFC Wimbledon narrowly beaten at Sutton, it opened the door for the Blues to overhaul the former side on goals scored to finish second in the standings.
Danny Cowley made eight changes from the side that beat Harrow to progress in the FA Cup at the weekend.
Sean Raggett was handed the captain’s armband, while Connor Ogilvie and Azeez also remained in the line-up.
Academy teenagers Adam Payce and Harvey Hughes were both handed senior debuts, while several more members of the under-18 side filled the bench.
Alex Bass returned between the sticks, with Kieron Freeman, Louis Thompson, Michael Jacobs, Gassan and George Hirst also started.
The young Eagles were first to threaten when John-Kymani Gordon wriggled his way into space and saw a shot deflected against the outside of the post.
But the Blues soon began to dominate proceedings and had a great chance to break the deadlock on 14 minutes.
Hughes’ clearance was flicked on by Gassan and Hirst raced away, taking a great touch to beat his man, but then getting the shot with the outside of his boot all wrong.
It then almost became a dream debut for Hughes, with the left-back hitting a low drive that Owen Goodman turned around the post.
The chances continued to come and Hirst was so close to opening his Pompey account after Gassan’s initial effort had been blocked.
He hit a low shot that appeared destined for the net, but Goodman got down to his right to make a superb save.
And the opening goal did finally arrive on 32 minutes, as Hirst and Gassan combined to find AZEEZ, with the Arsenal loanee calmly finding the net.
The lead was almost doubled soon after, with Thompson surging forward and laying the ball off for Jacobs, with the winger’s effort smothered by Goodman.
But Palace thought they had levelled after stealing possession and working the ball through to Rob Street.
The striker neatly curled his shot into the net and celebrated in front of the Fratton End, only to be cut short by an offside flag.
And the hosts had the final say of the first half, as Jacobs hit a fine shot that bent agonisingly past the upright.
Half Time: Pompey 1 Crystal Palace U21 0
Cowley made a change at the break, with academy midfielder Harry Jewitt-White replacing Thompson in the centre of the park.
Hirst’s hunt for a goal took him close again, as the striker showed neat footwork after collecting a Jacobs pass and sent a low shot inches past the post.
And the advantage was doubled on 54 minutes, when a fine right-sided cross from Freeman was smartly headed home by GASSAN.
Pompey continued to push forward in search of more goals and Hirst had an effort blocked, with the Eagles forced into some desperate defending.
The striker just did not have luck on his side and Goodman just about managed to scoop his header – from a Jacobs corner – off the line.
With AFC Wimbledon narrowly losing at Sutton, the Blues still required one more goal to reach the knockout stages.
They had to be alert at the other end, although Bass was not overly troubled by a low drive from David Omilabu.
Palace then went closer to getting on the scoresheet, as a Malachi Boateng thunderbolt cannoned against the post.
Pompey were still hunting for a goal of their own, though, and Hirst’s ambitious 35-yard strike flew straight at Goodman following a fine pass from Jewitt-White.
Another youngster was then introduced from the bench for the closing stages, with Payce making way for Alfie Bridgman.
Hirst went close again in stoppage-time, but his shot took a wicked deflection and sneaked just past the post.
But he did finally get the goal his overall performance deserved from the resulting corner that was taken by Azeez.
His delivery was helped on by Gassan and HIRST was able to bundle the ball home and celebrate in front of the Fratton End.
There was then a wait to see if Sutton would hold onto their lead over AFC Wimbledon before Pompey’s place in the knockout stages was confirmed.
Pompey (4-2-3-1): Bass; Freeman, Raggett (c), Ogilvie, Hughes; Thompson (Jewitt-White 46), Azeez; Payce (Bridgman 88), Gassan (Kaba 90+5), Jacobs; Hirst
Goals: Azeez 32, Gassan 54, Hirst 90+2
Subs not used: Steward, Setters, Howell, Gifford
Crystal Palace U21 (4-1-4-1): Goodman; D.Boateng, Quick, Rich-Baghuelou, Watson (Imray 76); M.Boateng (c); Omilabu, Kirby (Mooney 76), Roles (Taylor 57), Gordon; Street
Subs not used: Izquierdo, Thiselton, Sheridan, Cadogan
Referee: Will Finnie
Attendance: 1,660 (171 away fans)