Portsmouth claimed a deserved 2-0 victory at Gillingham thanks to two goals in three first-half minutes from John Marquis and Michael Jacobs.
After latching on to Ryan Williams neat backheel, former Gillingham loanee Marquis slotted past Jack Bonham for his first league goal of the season on 14 minutes.
Jacobs doubled the advantage after being put through by a spectacular half-volley pass by Marcus Harness, then cutting inside and poking home from close range.
Gillingham should have halved the deficit before the break but Vadaine Oliver's header from a Jordan Graham free-kick ballooned over the bar.
Kenny Jackett's side should have put the game to bed in the three minutes either side of half-time.
Tom Naylor's glancing header from a Ryan Williams cross hit the post in the final action before the break, then Williams saw his goal-bound shot brilliantly blocked on the line by Declan Drysdale.
The Gills, who haven't won a home league game on a Tuesday since November 2015, were nearly gifted a consolation when Lee Brown's attempted headed clearance almost ended up in his own net.