A lethargic Bognor performance brought their two-month unbeaten run to an end as a goal in each half gave a lively Grays the spoils at Nyewood Lane.
Nathan Ferguson gave the Essex visitors the lead and after Jason Prior’s strike had brought the Rocks level, sub Jordan Wilson found the winner 13 minutes from time.
The Rocks almost claimed a point when Prior struck the crossbar in the 89th minute but couldn’t avoid their first home defeat since October 4.
It’s a big dent in the Rocks’ hopes of sneaking into the play-offs but they have a quick chance to put the loss behind them when they go to Hampton and Richmond on Tuesday night.
The Rocks started the afternoon unbeaten in nine - their last defeat having come at Leatherhead on January 7.
Without Ollie Pearce, Stuart Green and Doug Tuck, Bognor started with Callum Overton partnering Jason Prior up front, with Harvey Whyte pushed forward into midfield and Pompey academy defender Snorre Nilsen at right-back.
The home side had an early somewhat half-hearted penalty shout when Alex Parsons tumbled under a challenge on the edge of the area. And as play quickly switched to the other end, Chris Winterton was hurt striker Domenka Demeka challenged him as he raced out of his area to clear a long ball.
Grays took the lead in the fifth minute when Correy Davidson’s cross from the right was not dealt with by the defence and Nathan Ferguson slammed the ball home (see the goal in the video on this page).
The Rocks were quickly back at Grays and Parsons was looking lively down the right. One ball into the box enabled Overton to flick on for Prior, but his shot on the turn was weak.
Another chance came when Parsons’ mazy run ended with Harvey Whyte reaching a ball just in time to power it into the six-yard box but it was blocked.
Charlie Oatway wasted a good opportunity on 16 minutes, mis-striking his shot after Nilsen’s clever cut-back from the right.
Bognor were doing most of the attacking and Prior was next to try his luck, but his low shot after a run across the defence was easy for keeper Connor Gough.
The Rocks won their first corner after 23 minutes but it was easily dealt with.
Parsons presented Demaka with a chance to run at goal but a well-timed tackle robbed him of the chance to shoot.
Oatway lashed a half-volley over the bar when a clearance following Jake Thomson’s free-kick fell to him (see video at the top of this article).
It looked odds-on to be 2-0 on the half-hour as Demaka broke with not a defender near him but Winterton stood up to him and blocked his low shot.
Demaka was giving Dan Sackman problems and the striker beat the Rocks man to a bouncing ball to try to lob Winterton, but the keeper athletically palmed it away.
Jay Leader miscued a 20-yard shot and watched as it ballooned up and over.
The Rocks’ play was becoming a little laboured but Parsons did rob his full-back to burst into the area. But his ball in towards Overton was cleared by a defender when Prior had looked the better-placed player for him to find.
Terry Dodd replaced Overton for the start of the second half as the Rocks looked to rise above the standards they’d managed before the break.
But it was Grays who had the first chance of the half, Davidson poking a shot beyond Winterton but just wide after another menacing Beaney run had played him in on goal.
When the Rocks finally did fashion a chance, with Whyte’s high cross falling nicely for Prior, he sent his header high and wide - and was offside anyway, which rather summed up the hosts’ day.
Grays ought to have doubled the lead when centre-half Manny Parry was unmarked as he met a free-kick into the six-yard box but the ball came off his knee and was grabbed by Winterton.
On 58 minutes, Thomson sent a wild shot clear of the clubhouse and into the car park.
But Bognor were back on level terms on the hour and it was old Dodd-Prior partnership that cracked it. Dodd held the ball up on the by-line and laid it into Prior, who ran across the box and fired a low left-foot shot beyond Gough’s dive to wake up the home crowd.
Dodd and Prior almost combined to put the Rocks ahead a minute later but Prior got in the way of Dodd’s shot and an offside flag went up.
A quick free-kick almost brought a second Rocks goal on 63 minutes as Grays argued it should not have been given. Then Whyte had to hobble off injured, and was replaced by new dual-registration signing from Havant, Harry Wedlake.
Grays also made a change, bringing on Jordan Wilson for Davidson.
Dodd, who had certainly livened up the hosts, weaved past two defenders to draw a fine save from Gough.
Another Grays change brought Quasi Marfu into the fray in place of James Stevens.
Grays retook the lead with a route-one goal. A long ball over the top caught the Rocks defence napping and sub Wilson controlled it and converted confidently past the advancing Winterton.
Oatway was replaced by Ryan Morey with ten minutes left.
Gray were as likely as Bognor to get the next goal and Demeka whizzed a drive just over the bar.
The last Grays substitution saw Mark Bentley replace Ferguson.
With a minute of the 90 left, Thomson was denied by the onrushing keeper and the loose ball fell to Prior, whose fierce shot cannoned back off the bar.
Rocks: Winterton, Nilsen, Crane, Oatway, Sackman, Robson, Whyte, Thomson, Prior, Overton, Parsons. Subs: Wedlake, Lawson, Dodd, Morey.
Grays: Gough, Morrison-Derbyshire, Silva, Leader, Parry, Stevens, Davidson, Beaney, Demeka, Ferguson, Carlos. Subs: Bentley, Little, Nouble, Wilson, Marfu.
Ref: David Spain