Mikel Arteta is nothing if not brave. With the outcome of their season hinging on their progress in the FA Cup after being dumped out of the Europa League, the Arsenal manager saw his faith in youth rewarded by a clinical away victory thanks to goals either side of half-time from Sokratis Papstathopoulos and Eddie Nketiah.

Against motivated opponents backed by a vociferous crowd, Arsenal rode the early Portsmouth storm and it took two flashes of inspiration from the returning Reiss Nelson to ease their path into the sixth round.

The forward – one of six players aged 20 or under who started here - was a constant menace down the right flank and totally justified his inclusion ahead of the £72m record signing Nicolas Pépé with a brilliant performance that showed Arsenal supporters there may be reasons to be positive about the future after all.

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“I’m pleased with all of them – the kids responded really well,” said a delighted Arteta. “I was looking at them in the 94th minute and they were still pressing and chasing. It’s a joy. I’m really enjoying working with them. They fully deserve the chance. I know it’s risky to play them in this competition but it’s worth that risk.”

With the FA Cup representing Arsenal’s last chance of silverware this season after their defeat by Olympiakos, Arteta surprisingly made nine changes, with the Spanish defender Pablo Marí handed his debut. Nelson returned from injury to make his first start of the year in a youthful attacking trio alongside Gabriel Martinelli and Eddie Nketiah. Arteta admitted his team selection had been influenced by the Europa League defeat that had left several of his senior players “still hanging on what happened”.

He had been similarly bold in selecting his emerging crop of young players in the ruthless victory at Bournemouth in the last round but against a Portsmouth side who had won their last 10 home matches in all competitions, this trip to Fratton Park was always likely to be a more testing occasion.

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Not since the infamous defeat to Wrexham in 1992 have Arsenal been eliminated from the competition by a team from outside the top two divisions but in Kenny Jackett, their rookie manager was up against someone with real pedigree in the FA Cup.

The former Wales midfielder played for Watford in the 1984 final and also guided Millwall to the last four in 2013, with Portsmouth having already seen off four teams to reach this stage.

Third in League One and chasing a return to the second tier for the first time in nearly eight years, there is a positivity around the club not seen since the 2008 FA Cup triumph and it was reflected in the bouncing atmosphere at the kick-off.

Facebook Twitter Pinterest Sokratis Papastathopoulos (second left) volleyed Arsenal into a 1-0 lead just before half-time. Photograph: James Marsh/BPI/Shutterstock

Despite making six changes from the win over Rochdale on Friday that included leaving the captain, Tom Naylor, and the top scorer, Ronan Curtis, on the bench, it was not hard to see how Portsmouth have put together such an impressive record at this old ground given the way they started.

Arsenal did well to withstand the early barrage and Lucas Torreira was withdrawn after quarter of an hour following a bad challenge from James Bolton and the midfielder left the ground on crutches with his ankle in a brace.

Portsmouth continued to make the running as they were serenaded with chants of “We’re our way back” from three sides of the ground, even if they failed to really test Emiliano Martínez in the Arsenal goal.

Matteo Guendouzi’s harsh booking for placing the ball on the pitch in an over-deliberate manner as he took a free-kick would have done nothing to improve Arteta’s mood as half-time approached but a brilliantly composed finish from Papstathopoulos in first-half injury time from Nelson’s pinpoint cross settled his nerves at just the right time.

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“We needed those moments in the first half to go for us,” Jackett said. “We disappointed not to go in at 0-0. That deflated us.”

Tony Adams, who was the assistant manager to Harry Redknapp in 2008 before taking over a few months after their famous triumph at Wembley, was introduced at half-time to a rapturous reception from both sets of fans. He also lifted the FA Cup three times with Arsenal and will have been impressed with the way the side he captained with such distinction for 14 years put the tie out of reach within six minutes of the second half.

Fittingly in the city synonymous with his maritime namesake, once again it was Nelson who provided the ammunition after leaving his marker, Steve Seddon, for dead to allow Nketiah to bundle home at the near post.

Jackett threw on boyhood Arsenal fan Curtis and striker partner John Marquis in a last throw of the dice but Portsmouth struggled to exert the kind of pressure they enjoyed in the first half, with Bukayo Saka’s shot almost extending Arsenal’s lead as the clock ticked down.

Portsmouth know their main priority is to achieve promotion, while Arteta will take heart from the way his new-look defence saw out this victory with minimal fuss after all the last-minute drama against Olympiakos.