The 23-year-old for Hampshire 2nd XI and Somerset 2nd XI batsman hit 104 in a team total of 225-5 at Allotment Road.
That was two more than Sarisbury’s 11 players could muster between them as Portsmouth claimed a fourth SPL victory of 2021.
It was Duggan’s seventh SPL hundred with his first for Portsmouth coming against former club Ventnor - 111 - in May 2019.
Previously, he had scored five SPL top flight centuries for the Hampshire Academy, including four in 2015, the year he won the ECB Southern Premier League Young Cricketer of the Year award for scoring 761 Premier Division runs.
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Duggan also played alongside Tom Scriven and Harry Came in the Hampshire side that won the Under-17 County Championship that year.
Duggan, who was skippering Portsmouth against Sarisbury in the absence of James Christian, won the toss and elected to bat.
He put on 117 for the first wicket with Jordan Palmer-Goddard, who hit 51 on his third SPL appearance of the season - he had scored 72 against Burridge 2nds in his second game - and 79 with Jack Marston (45) for the third wicket.
Duggan was eventually run out by Sam Hill having hit nine fours and a six in his 118-ball stay at the crease.
Andrew Marston (3-12 off eight overs) did the initial damage when Sarisbury replied, dismissing openers Ricky Rawlins (25) and Will Bolton (22).
Athletic reached 78-2 in reply before the game swung rapidly Portsmouth’s way when three wickets tumbled for no runs.
Dan Wallis clean bowled Jack Lovett and Sam Floyd and Marston rearranged the stumps of in-form captain Josh Hill (9).
Wallis went on to claim a career league best 5-22 - the first time he had taken five wickets in an innings - as the hosts lost their last eight wickets for 24 runs to subside to 102 all out.
It was a fifth defeat in seven games for Sarisbury, who are second bottom at the halfway stage of the season.