The visitors went on to crash to a 5-0 defeat - the ninth time they had conceded four or more in a game during their debut step 5 campaign.
Tom Grice’s side have now picked up just two points in their last 10 games, and have scored just once in their last seven outings.
The club’s latest hammering came hard on the heels of having three points docked by the league for fielding an ineligible player.
They had played Jeffes against Cowes on December 18 a week after he had been dismissed, ironically in a home loss to Blackfield.
Normally, if a player is sent off on a Saturday, the suspension starts the following weekend. But USP played Jeffes against Cowes - in a match they won 4-1 - as they had not had confirmation regarding the ban.
As it turned out, that confirmation duly arrived the following day. USP still didn’t see any potential problems and left Jeffes out of their next game - a 3-1 loss at Horndean in early January.
But at a hearing last week, they were found guilty and docked three points, dumping them into the bottom five.
‘It’s extremely frustrating,’ said boss Tom Grice. ‘I don’t get involved in the admin - I just get told who can and cannot play. And we hadn’t heard anything on TJ (Jeffes) so we played him. Bob (Brady, USP secretary) tried to speak to the FA at the time but couldn’t get hold of anyone.
‘If anything, this shows that if there is an element of doubt, then don’t play them.
‘It’s farcical - the whole thing should be dealt with much quicker.’
Jeffes’ third red card came just three weeks after his second, in a 4-0 home loss to Shaftesbury.
He was dismissed for fouling former AFC Portchester striker Owen Fee just outside the penalty box.
USP were trailing to a single Alex Andrews goal at the time - the result of a first half corner from Fee that Grice described as ‘the worst ever’, a low flag-kick that his side failed to clear.
Fee struck twice after Jeffes saw his latest red, leaving Grice to admit: ‘Once you concede two or three, heads go down.
‘We are low on confidence, having not won since the end of January.
‘It was a very, very, very tough afternoon - you don’t want to lose 5-0 to a team in and around where you are in the table.’
USP could yet finish in the bottom four, but Grice said: ‘The aim was always to stay in the league this season. There’s clubs with more money than us who have struggled.
‘There’s a big gulf between the bottom half and the top half … it’s been a very, very tough last two and a bit months.’
Jeffes will start another suspension when USP bring the curtain down on their league season at Bournemouth Poppies next Saturday.
Midfielder Ryan Smart is also out after suffering a fractured ankle in the first half at Blackfield.