Sokratis and Eddie Nketiah were on target as we eased into the last eight of the Emirates FA Cup.
We took the lead with a centre forward's finish from a centre back playing at right back.
Our Greek defender was the goalscorer, volleying in Reiss Nelson's pacy cross on the run after Dani Ceballos had picked out Nelson on the right.
That was pretty much the last action of the first half - and we gave ourselves a cushion early in the second half.
Nelson was again the provider, bursting down the right to cross for Nketiah, who reacted in a flash to find the roof of the net after his first attempt to finish was thwarted.
That goal finally took the wind out of Portsmouth's sails after what was a breezy opening from the League One side.
Roared on by a boisterous home crowd, they targeted the right side of our defence and caused problems through Marcus Harness and Steve Seddon.
For all that, Emi Martinez had little to do with debutant Pablo Mari and the impressive David Luiz defending with composure.
We looked comfortable after Nketiah's goal and could have added more through Nelson and Bukayo Saka.
All in all it was a positive night, but there was one negative - Lucas Torreira was stretchered off in the first half.
HOW IT HAPPENED
THREE THINGS WE NOTICED
WHAT IT MEANS
We're in the draw for the FA Cup quarter-finals and will find out our opponents on Wednesday.
Mikel Arteta freshened up his starting line-up following that energy-sapping defeat against Olympiacos in the Europa League.
Only David Luiz and Saka kept their places while Pierre-Emerick Aubameyang and Mesut Ozil were rested completely.
Of the nine changes, the most notable was Pablo Mari. He was brought in to make his first-team debut.
The Premier League returns on Saturday with a London derby with West Ham at Emirates Stadium.
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