Early on a forward ball was headed inside by Lucas Pattenden who picked out Trialist 1 after just 2 minutes but he was deflected wide with his advance.
Then Mather received the ball on the edge of the box but after advancing into the penalty area he stubbed a left footed effort wide.
Ryan Hall had to dash out of his area to deal with Karim Haitham’s forward lofted pass over the defence. Steve Hutchings was chasing it but the goalkeeper got there first on 10 minutes.
Tommy Lee Higgs stole possession on the right hand flank before running across the edge of the area. His shot got a deflection wide, winning a corner but the ball in was headed away at the near post.
Kieran Douglas tripped up a player on the attack and went into the book after just 14 minutes.
Bognor’s defence were having to block multiple chances with Haitham getting blocked with low efforts on at least two occasions in quick succession.
Then Haitham was running at goal again before Craig Robson slid in to stop him in his tracks on 18 minutes.
Trialist 1 did well to get to the ball and draw the foul on 27 minutes on the right flank. Calvin Davies swirled the freekick in but Douglas couldn’t get to it and he went to ground under pressure from the Chichester defender.
Ben Anderson did well to win the ball in the Chi half. He ran through and combined with Higgs before hitting one himself and forcing Kieran McGee into a diving save, pushing the ball around the post on 31 minutes.
But Rocks opened the scoring on 33 minutes. A ball out wide found Pattenden in space and he used his pace before cutting the ball back along the deck to De St Croix who composed himself before coolly slotting the ball low into the bottom corner.
On 41 minutes De St Croix chipped the ball into the area from the left and found Mather unmarked but his header was hit into the ground and easily saved by McGee.
Eric Dellaud, the new signing, received the ball square before belting it low and again McGee was called into action pushing it around his right post on 42 minutes.
Another goal came for Bognor on 43 minutes. Again, Pattenden was there to tee him up with a neat incisive pass to Mather who hit it powerfully and despite McGee’s efforts on the line, couldn’t stop it from going in.
Dellaud did very well to head out a clearance into the path of Mather. He ran on, was blocked with his chance, and then Dellaud’s follow up was also blocked. But Higgs was up with him to divert the ball into the net in the 4th minute of first half stoppage time.
Isaac Olaniyan made good headway on the left before Trialist 2 made a run but his pass back square to De St Croix saw the midfielder scoop his chance high over the bar.
Then Anderson was back to clear up the mess as Ethan Pritchard had beaten Ryan Hall to the bouncing ball but his low effort was cut out by Anderson along the deck.
Davies picked out Olaniyan with a dipping corner. Olaniyan was outstretched though when he diverted the ball towards goal. But McGee easily stopped that one.
Haitham did well to latch onto the bouncing ball over Danny Howick but his shot was feeble and easily stopped by Hall.
De St Croix neatly chipped the ball over defence for Trialist 2 who composed himself, committed McGee into a dive to his left but the ball rolled wide of the right post.
Hall was called into action as Pritchard found himself with the ball on 55 minutes just in front of goal but his low strike was denied by the Rocks goalkeeper.
Trialist 2 found Anderson the right overlap. He got a decent low cross in but the Chi City defence spun the ball over the crossbar.
Olaniyan did well on the left and a swift turn saw him pick out Mather along the deck and he diverted it in on 70 minutes to extend Bognor’s lead.
A trialist for Chichester saw Hall have to punch the ball out of the area under pressure in the air.
A lack of communication at the back by Howick and Hall saw both get mixed up to allow Haitham to knock the ball low into an empty net on 76 minutes.
Ben Pashley went into the book on 81 minutes after his reaction to a clear foul on Trialist 2 for Bognor on the touchline.
Davies did well to dig out a cross which was headed out to Mather who struck it with his first touch. It was always rising though over the bar on 86 minutes.
Dellaud did very well on the left to cut out an attack from Chi before passing it forward to Mather on the turn. But after beating his man, he stubbed the ball into the turf and wide from an angle on 89 minutes.
Haitham had another chance on the rise after a cross from the left in stoppage time. But it was hit straight at Hall.
Bognor were the stronger of the two sides and finished 4-1 after nearly 5 minutes of stoppage time. They welcome Flansham Park Rangers next on Friday 4 August at the earlier kick off time of 7pm.
Rocks: Hall, Anderson, Dellaud, Davies, Douglas (Howick 45), Robson (Mason 45), De St Croix (McCormick 65), Trialist 1 (Olaniyan 45), Mather, Higgs (Trialist 2 45), Pattenden (Holland 71)
Unused Sub: Smith