Potters Bar ended the Rocks' all-too-brief winning run with a 4-0 Isthmian premier victory at Nyewood Lane - with their second and third goals down to basic errors by debut-making keeper Myles Roberts.
Roberts, on loan from Reading, is the fourth keeper Bognor have used this season but his bow was one to forget as he gifted visiting striker Ben Ward-Cochrane the second and third goals of a hat-trick which swept his side to victory after a goalless first half.
It got worse for the Rocks in the closing stages when Thomas Gogo got a fourth for the visitors, this one after poor defending on the Rocks left. It's a big disappointment for the Rocks after they won - and won well - their previous two home games.
And it gives them a problem position that seems to need more work, with Roberts the third keeper of the four they have used this season to have made crucial mistakes leading to goals.
Bognor went into the game on the back of an improved run of form – having won their past two games, 2-0 at home to Haringey and 5-1 at the Lane versus Leatherhead.
They gave a debut to the fourth goalkeeper they have used this season, Myles Roberts, on loan from Reading. He had initially joined on loan a fortnight ago but his Rocks bow was delayed by a training ground injury.
Otherwise the Rocks had a virtually full squad to pick from and added ex-Pompey youngster Eddie Wakley, a defender, to the subs' bench on a day when there was rain at the Lane, keeping crowd numbers a little lower than they might have been on Non-League Day.
Pompey academy duo Brad Lethbridge and Joe Hancott both started for Bognor four days after they played for the Blues' first team in the Football League Trophy at Oxford – with Lethbridge scoring one of their goals in a 2-2 draw.
There was little to excite in the opening 10 minutes but Potters Bar were close to going ahead with the Rocks indebted to Hancott for clearing a glancing header from a corner off the line. Roberts saved the follow-up shot at the second attempt.
The Rocks were playing neat football in places with most of their best work coming down the left through Hancott and Lethbridge. But the Hertfordshire visitors stood strong at the back and keeper R'avan Constable was not called into serious action.
A Tommy Leigh free-kick into the box was nodded down into the goalmouth by Keaton Wood but Constable collected it.
The game's first booking went to Rocks centre-half Joe Cook on 26 minutes after stopping Thomas Gogo in an attack down the Potters Bar left.
Bognor carved out a decent opening on 28 minutes when Jimmy Muitt beat his man down the right and crossed for James Crane, whose volley was straight at Constable. It was an improvement for the Rocks as they tested the stopper for the first time.
Bognor were having to play patiently, with Bar getting back in numbers each time the Rocks progressed into their halves. The sideways and backwards passes were certainly outnumbering the forward balls.
There was brief excitement when Lethbridge chased a through ball and Constable came out of his area to collect it before having to follow it back in to dive on the ball and pouch it.
Dan Smith nodded a long ball back to Doug Tuck 25 yards from goal but his effort flew well over the bar. Muitt woke up a lethargic crowd with a quick run and shot that whistled the wrong side of Constable's post.
The best Bognor chance of the first half came in injury time. Muitt beat his man down the right and crossed to an unmarked Leigh at the far post but he took too long to control it and the chance was gone – and when it fell to Lethbridge his shot was off-target. HT 0-0
Bognor played themselves into a spot of bother five minutes into the second half as Wood and Roberts were hurried into a clearance by the keeper that went straight to Ryan Young, but Potters Bar couldn't take advantage.
From nowhere, Potters Bar took the lead on 54 minutes and it was all too easy. With Joe Cook seemingly appealing for offside, a quick pass put Ward-Cochrane in on goal and after drawing and rounding Roberts, he took his time before slotting the ball past a defender who'd got back on the line. It was a blow for the Rocks after they had defended so well in the first half.
The referee ignored some shirt-pulling by Potters Bar at a corner but didn't ignore a foul by Muitt as the visitors broke, and the Rocks man was booked. As Bognor looked for an equaliser Harvey Whyte's high pass sent Muitt scuttling away down the right but his cross was an easy catch for Constable.
Bognor responded well to going behind and Crane got to the byline for a cross that fell to Tuck, but his shot was deflected behind for a corner.
Lethbridge still looked Bognor's best outlet – one run down the left ended with the ball going out for a goal-kick, the second led to a Muitt corner from which Lethbridge himself glanced a header goalwards but saw it nodded off the line by Young.
It was 2-0 in the 72nd minute and you had to feel sorry for debutant keeper Roberts as he came out to the edge of his area to collect a through ball only to let it go of it, allowing Ward-Cochrane to flick in his second from the edge of the area.
Bognor went straight on the attack and Whyte's fierce shot from 20 yards took a deflection for a corner, which came to nothing.
Ashton Leigh replaced Lethbridge with 14 minutes to go and within seconds Ward-Cochrane had his hat-trick and it was another error by Roberts, who rolled the ball out too far to allow the striker to nip in and take advantage.
Potters Bar made a change with 10 minutes to go, George Nicholas replacing Imedd Kartita.
Sub Leigh almost helped Bognor get one back with a cross into the six-yard box but neither Smith nor Cook could force it home.
Ben Eden-Clark came on for Crane with eight minutes left.
Rocks MoM was named to skipper Whyte – shortly before more soft defending led to a fourth for Potters Bar, put away after a run into the box by Gogo after a loose bit of play by Hancott on the left.
Roberts did make an excellent save in five added-on minutes to deny Young, who ran through on goal as the home defence went to pieces.
A booking for Tuck was the last frustrating act of the afternoon for the unhappy home team.
Rocks: Roberts, Crane, Hancott, Tuck, Cook, Wood, Whyte, Leigh, Smith, Muitt, Lethbridge. Subs: Clark-Eden, Leigh, Scutt, Hensel, Wakley.
Potters Bar: Constable, Doyle, Lomas, Cole, Humphrey, Quarrington-Carter, Young, Craddock, Ward-Cochrane, Kartita, Gogo. Subs: Ehui, Constantinous, Nicholas, O'Leary.
Ref: Shelby Elson