The Premier League leaders, fresh off a goalless draw against Liverpool and facing a grueling run of four successive away games in different competitions, made 10 changes to their lineup. Mikel Arteta handed starts to fringe players and youngsters, with Christian Nørgaard captaining the side and Noni Madueke, Eberechi Eze, and Ethan Nwaneri adding flair in attacking areas.
But it was far from straightforward for the visitors. Portsmouth, battling relegation fears in the Championship and coming off a heavy defeat to Bristol City, stunned the Emirates faithful by taking a shock lead in just the third minute. Colby Bishop pounced on a rebound to fire past Kepa Arrizabalaga, igniting a raucous atmosphere at a sold-out Fratton Park (attendance: 20,611).
The home fans dreamed of a historic upset — Portsmouth hadn't beaten Arsenal since 1958 — but the Gunners' class shone through. Arsenal leveled in scrappy fashion on 8 minutes when an Eberechi Eze corner was bundled home via an Andre Dozzell own goal under pressure from Christian Nørgaard.
Martinelli then took center stage. The Brazilian winger, who had faced criticism following a heated incident in the previous league game, responded in the best way possible. He rose highest to head in Noni Madueke's corner on 25 minutes, giving Arsenal the lead despite protests over a potential goal kick.
Arsenal dominated possession but missed chances to kill the game before halftime — most notably when Madueke dragged a penalty wide in the 43rd minute after a foul on him.
The second half belonged to Martinelli. On 51 minutes, a quick-thinking free-kick from Myles Lewis-Skelly caught Pompey napping, allowing Gabriel Jesus to tee up the winger for a simple tap-in. Martinelli completed his treble on 72 minutes with another pinpoint header from Madueke's corner — Arsenal's third set-piece goal of the afternoon, highlighting their deadly threat from dead balls (17 corners goals this season already).
Portsmouth fought bravely, pushing forward despite finishing the game with 10 men after a late hamstring injury to one of their substitutes, but they couldn't find another breakthrough. Kai Havertz made a welcome return from long-term injury off the bench, while 16-year-old Marli Salmon etched his name in the history books as Arsenal's youngest-ever FA Cup player at 16 years and 135 days.
This comfortable victory sees Arsenal safely into the fourth round, keeping their quadruple hopes alive amid a packed schedule. Next up: the Carabao Cup semi-final first leg at Chelsea on Wednesday, followed by trips to Nottingham Forest and Inter Milan.
Martinelli's treble not only secured the win but also provided the perfect riposte to his critics. As one fan put it: "Haters gonna hate — he just bags three to shut them up!"
A statement performance from the Gunners when it mattered most. The magic of the FA Cup lives on — and Arsenal remain very much in the hunt for silverware.