Albion slumped to their sixth straight defeat and third at Withdean to continue their sorry return to the First Division.
Hinshelwood must be scratching his head to understand the amount of silly and uncharacteristic mistakes which his side are gifting their opponents.
He knows they must learn one lesson fast if they are to avoid relegation come May - it is one thing to give away an early goal at home to lowly Exeter, but teams playing at the higher level of Division One, especially those with realistic ambitions for promotion to the Premiership, will punish you.
Careless defending contributed to Paul Shaw stroking the Gills ahead in the 11th minute.
But before there was time for the gloom to once more descend over the Seagulls faithful, David Perpetuini doubled the deficit less than a minute later with an angled left-foot drive.
Richard Carpenter's right-foot shot from 20 yards in off a post against his old club ended Albion's Withdean goal drought this season, but Shaw restored the two-goal cushion with an assured chip over Andy Petterson.
Referee Mark Cooper became the centre of attention after that. The shaven-headed man mountain from Walsall sent-off Gillingham's deputy rightback Mark Saunders in the 37th minute for retaliating to a two-footed tackle by Shaun Wilkinson which warranted a booking.
The Seagulls pressed forward relentlessly throughout the second half against the ten men and were rewarded ten minutes from time when the fit-again Gary Hart stretched to volley in a cross from fellow half time substitute Daniel Marney.
The lively Marney fired over an equalising opportunity from six yards before a richly entertaining contest was capped by a comical finish.
Kevin James raced clear of Robbie Pethick on the break. Petterson slipped on the pre-watered pitch as he advanced, then lost his footing again in retreat as James slotted into the vacant net.
The former Gillingham youngster dashed over to the visiting fans in the north-east corner, removing his shirt in celebration. Cooper regarded that as a second bookable offence and red carded him as well.
Card-crazy Cooper also cautioned seven other players. Andy Hessenthaler, the Gills' player-manager, branded his performance an "absolute disgrace" during a post-match tirade which is bound to land him in trouble.
Hinshelwood said: "We cannot prepare right in the week and then give away sloppy goals like that. It left us a mountain to climb.
"We didn't deserve to win the game on our first half performance."
Maybe not, but he deserves longer than Knight has indicated he will give him to put things right.
- Albion (4-4-2): Petterson (gk) 6, Watson (lb) 6, Cullip (cd) 6, Butters (cd) 6, Oatway (cm) 6, Carpenter (cm) 8, Pethick (rb) 6, Jones (lw) 6, Wilkinson (f) 6, Melton (rw) 6, Kitson (f) 6. Subs: Rogers, Hart 7 for Melton (withdrawn 46), Packham, Marney 7 for Wilkinson (withdrawn 46), Hammond for Jones (withdrawn 86).
- Scorers: Carpenter (27), Hart (80).
- Bookings: Oatway (29) foul, Jones (29) dissent, Butters (45) foul.
- Half-Time: Albion 1 Gillingham 3.
- Attendance: 6,733.
- Fan's View: Barry Render (Shoreham).
- Barry Render (Shoreham) The long-awaited league clash between the Gills and their former squatters was as good as over when the Seagulls yet again conceded two early goals.
A cracking shot by Richard Carpenter kick-started the Albion on the half-hour but a third goal by the Gills just before half time sealed their victory.
The ref maintained his high profile by sending off two players and booking eight in a match that wasn't particularly physical.
How can you take any positives from a 4-2 reverse at home against a team with more injury problems than us?
Well, Gary Hart is back, scored and hopefully Kuipers and Zamora won't be far behind. Dick Knight said on SCR not to panic, so I'm not ... yet.
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