Portsmouth produced a monumental defensive effort to come away from Winchester with a 13-5 London two south win under their belt.
The impressive victory saw the Rugby Camp club leapfrog their hosts into joint-third place.
It also meant they avenged a defeat earlier in the season when Winchester won in Portsmouth.
Delighted coach Ben Dudley felt the excellent result showed just how far his team have come since the start of the season.
They have been in strong form in recent weeks after the difficult opening to the campaign.
He said: ‘After starting the season with three defeats on the bounce we have won seven drawn one and lost one game,’ said Dudley.
‘We have to be pleased with that.
‘This was another good performance on a horrible day in awful conditions.
‘Winchester had done well to get the game on but the pitch was barely playable.
‘At times Winchester had us pinned back but our defence was monumental.
‘We just kept putting in the hits, getting back to our feet and putting in some more until we turned the ball over.
‘The improvement in that area of the game is very pleasing.
‘Our communication was better, players are understanding their roles and trusting each other a lot more.’
Simon Morgan put Portsmouth ahead with an early penalty and the visitors extended their lead on the stroke of half-time.
Winchester were having one of their better attacks when Portsmouth managed to turn the ball over.
Luke Simmons fly-hacked the ball ahead and outpaced the defence to get the touchdown, with Morgan converting to give the visitors a 10-0 lead at the interval.
Despite all their pressure the hosts could only score one try in the second half with Morgan slotting a late penalty in reply.
‘We are still quite a young side and made life difficult for ourselves by trying to run the ball out at times,’ said Dudley.
‘It was tough to keep hold of the ball in the conditions and that allowed Winchester to put us under pressure.’
In London three south west, United Services Portsmouth slipped to a 26-9 defeat at Old Mid-Whitgiftian.
Hampshire one strugglers Locks Heath Pumas and Petersfeld both suffered further defeats.
Pumas lost 28-16 defeat at Fordingbridge.
And Petersfield went down 33-15 at Ellingham & Ringwood.