Portsmouth saw their London two south west survival hopes hit by a 17-13 defeat against Winchester at Rugby Camp.
Captain Greg Hoolihan almost capped an inspiring display with a last-minute try.
But the home side paid the price for missed chances.
After Winchester were reduced to 14 men early in the second half, the hosts missed several clear try-scoring opportunities.
They also failed with two conversions and hit the post with a penalty.
Manager Nigel Morgan felt Portsmouth more than played their part in the match.
He said: ‘It was a cracking game and could have gone either way.
‘Both teams will feel they did enough to win it.
‘After an awkward opening 10 minutes when we couldn’t get hold of the ball, we went on to dominate the set-pieces.
‘Our forwards performed well and they had what we felt was a perfectly good try disallowed in the second half.
‘They went over the line from a catch and drive at a line-out only to be penalised for blocking.’
Winchester raced into a 10-point lead in the opening 10 minutes.
Portsmouth began to find their way and a Lee Chandler dropped goal got them on the board.
A poor start to the second period from the visitors, though, allowed Winchester to stretch their lead to 17-3, leaving Portsmouth with it all to do.
On 53 minutes, the visitors were reduced to 14 men.
Their second-row forward was sent off for violent conduct.
From that point Portsmouth took charge of the game and began to fightback through an Adam Long try.
Eight minutes from time, replacement centre Gareth Richards made a superb break only to be stopped close to the line.
Supporting forward Darren Crabb, however, was on hand to pick up and dive over the line for the try.
Hoolihan almost snatched the win with a terrific break down the touchline.
The hooker chipped the ball over the last defender but saw it roll agonisingly into touch before he could regather it.
‘Disappointingly, we missed both the conversions and that proved our downfall,’ said Morgan.
‘It is frustrating because we could so easily have come away with a win.
‘We have to be far more clinical and ruthless when we get our chances.’
‘The relegation issue looks like going to the wire. It is all going to change at the bottom, week by week.
‘It is a question of keeping our nerve between now and the end of the season.
‘We will need to find our kicking boots to help improve our chances.’
Portsmouth’s fight to stay up continues with a vital clash at Old Alleynians on Sunday.
United Services scored five tries as they strengthened their Hampshire one promotion bid with an easy 36-7 win at Romsey.
Steve Gee scored two tries, while Danny Johnson, Martin Hoskin and Will Rolfe also crossed the whitewash.
Chris Marriott impressed with the boot, kicking four conversions and a penalty.