USP slipped to a 3-0 home defeat at the hands of Alton - just five days after the teams battled out a 3-3 draw in their Wessex League Premier Division opener.
Grice was furious with what he felt was a 'lacklustre' display from his players.
The USP boss tore into his team following the defeat - and is now demanding a big response as they get set for a trip to Alresford on Saturday.
‘It wasn’t good enough, nowhere near good enough, nowhere near the levels we set at training and nowhere near the levels we completed our pre-season at,’ Grice bemoaned.
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‘The players are better than that and that’s what disappoints me the most.
‘It felt like there were a few out there who didn’t really want to be there, if I’m being completely honest.
‘All in all, it was not a good day at the office - I know it’s a cliché thing to say, but it’s important that we don’t let that roll onto Saturday at Alresford.
‘I’m furious, to be honest, I can take being beaten by the better team but what I can’t take is lacklustre performances and that’s exactly what it was.
‘We made a few formational changes and I held my hands up at half time - we didn’t set up right.
‘You can make all of the adjustments in the world, but if you’ve got players out there not giving 100 per cent you will lose and that’s exactly what happened.’
USP went in at the break 1-0 behind after Jack Fowler's 20th-minute opener.
The tie was then put beyond US Portsmouth as they conceded twice in a four-minute second half spell.
Rob Carr doubled Alton's advantage on 66 minutes before rounding off the scoring 20 minutes from the end.