Gabriel Martinelli scored a hat-trick at Fratton Park as Arsenal avoided an FA Cup upset against Championship side Portsmouth.

The visitors, a point above relegation in the second tier, took an early lead through Colby Bishop in the third minute. Kepa Arrizabalaga saved Connor Chaplin's effort, with Bishop converting the rebound.

Arsenal were level five minutes later, as the first of three set-pieces to result in a goal found its way in off Portsmouth's Andre Dozell for an own goal, under pressure from Christian Norgaard.

Martinelli's flicked header from another corner but the Gunners in front, before Noni Madueke missed a penalty after the England winger was fouled by former Arsenal academy graduate Zak Swanson.

Myles Lewis-Skelly's quick free-kick saw Gabriel Jesus find his compatriot Martinelli, who made it 3-1 six minutes into the second half.

In the 72nd minute, Martinelli completed his hat-trick with another front post flicked header from a corner to seal Arsenal's passage into the fourth round.

Kai Havertz was introduced from the bench in the second half to mark his return from injury, with involvement for 16-year-old Marli Salmon as well.