The Royals had both Owen Roundell and Jake Raine shown straight red cards, while the hosts saw Luke Perkins dismissed following an incident involving the trio minutes before the break.
Portchester boss Dave Carter brought off leading scorer Kieran Roberts and George Barker, who had fired the visitors ahead, at the break and the pair were replaced by defender Zak Sharp and debutant Aaron McCreadie to provide some defensive-minded cover after the double sending off.
But the Royals were able to preserve the two-goal lead Barker - firing home his fourth goal in three games - and Lee Wort had given them before the break and prior to the three red cards.
In the end it proved to be another step in the right direction for Portchester, who followed up their first league win of the season at Bournemouth on Saturday with another crucial three points.
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n Fareham Town made it three Wessex League Premier wins on the spin with a 2-0 victory at Hamble Club.
Fresh from back-to-back successes over Hythe & Dibden, first-half strikes from Simon Woods and Kai Sterne ensured Pete Stiles' men secured another three points.
Woods bundled the Reds in front, reacting quickest after Curt Robbins' spot-kick had been saved inside seven minutes.
Sterne was then on hand to fire home from outside the area six minutes before the break to wrap up victory.
n US Portsmouth showed their battling qualities to pick up a point at Alresford.
George Roy levelled for USP eight minutes after the break after the hosts took an early lead.
With time running out, captain Tom Jeffes fired home a second leveller a minute from the end as it ended 2-2.