Goals from James Bolton and John Marquis secured safe passage for Pompey.
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Portsmouth triumphed in an all-League One FA Cup battle as they eased to a deserved 2-1 win at Fleetwood.
Both Pompey goals came in a decisive five-minute spell midway through the second half as they reached the fourth round for the second consecutive year.
Portsmouth went close after three minutes when James Bolton headed Marcus Harness' pinpoint cross inches wide.
The visitors' Andy Cannon then crashed a half-volley narrowly over after he pounced on a poor defensive header from Harry Souttar.
Fleetwood's first chance came in the 33rd minute when a Paddy Madden shot was well saved by Alex Bass after he met Ched Evans' through-ball.
Shortly before the break Souttar rose well but headed Paul Coutts' corner over the crossbar.
Fleetwood had the first chance of the second half when Madden fired over from just inside the box.
Pompey broke the deadlock in the 66th minute when Bolton bundled home Ronan Curtis' inswinging corner from close range.
It was 2-0 five minutes later as John Marquis forced home from close in following a Christian Burgess header into the danger zone.
Fleetwood substitute Conor McAleny fired home a deflected shot in stoppage time, but it proved too little, too late.