A battling performance from a dogged Rocks saw them get their own back on the Scholars, who won 4-0 at Nyewood Lane earlier on in the season.
It was Lethbridge's second winner in eight days after he got the crucial goal in the 4-3 win at home to Folkestone.
Boss Jack Pearce fielded centre-half Joe Cook after he returned to play for the Rocks for a second loan spell from Havant while ex-Burton and Southampton player Jake Flannigan got a start in midfield with Josh Flint missing.
Tommy Leigh's early corner on the left saw him float the ball just beyond Cook. Dan Smith ran on to a forward pass before shooting twice against defenders inside the box as Bognor tried to get to grips with a bobbly surface against the Scholars.
Lethbridge hit a cross in from the left but R'Aven Constable in the Potters Bar goal gathered it high in the air. Keagan Cole hit a free-kick into the area but Amadou Tangara got there. Leigh found Smith on the run before Ben Ward-Cochrane found Ryan Young who hit one from the edge of the box - forcing Tangara into a fine parried save on 18 minutes.
Good work from Lethbridge on the left saw him find Flannigan but his cross flew over the bar. Mason Walsh slipped up and took out Andrew Lomas inadvertently in the area as he tried to beat him. A corner was headed off the line at the near post by a Bognor defender seconds later.
Doug Tuck did well to find Lethbridge but he fired a shot off a defender. Then another cross by Lethbridge was well gathered by Constable. Ward-Cochrane's effort was blocked by Matt Casey. Bradley Sach slammed a low shot at goal, forcing Tangara into a reaction save deflecting it out for a corner on 32 minutes.
Cook got Bognor on the attack before Tuck played it out wide to Lethbridge, who struck it high - just beyond the frame of goal on 35 minutes. Josh Hutchinson won a corner that was headed clear by Leigh. Sach sprang on the attack but his cross was too much for Ward-Cochrane on the back post. HT 0-0
Smith took a knock to the back of the head as play kicked off for the second half. Constable had to punch clear a cross from the right as Bognor started brightly. Bognor took the lead on 50 minutes as a cross from the right bounced through to an unmarked Lethbridge, who cut inside before driving it low into the net off a flailing Constable arm.
Hutchinson put a chance over the bar when it seemed easier to get it on target. Lethbridge curled the ball straight on to the head of Smith but the striker nodded it straight at Constable. Lethbridge was full of confidence after netting the opening goal and he got another shot away after driving inside the pitch before smashing it wide.
Flannigan won a free-kick. Leigh played a diagonal ball into the box from the free-kick and found Casey but he had strayed offside. Tangara was beaten on the break as Ward-Cochrane got to the ball and with an empty net but he could only kick a shot wide on 60 minutes. James Crane went into the book for delaying a throw in on 61 minutes as the game reached boiling point.
Harvey Whyte got a straight red card on 63 minutes with a sliding challenge on Young - despite winning the ball the referee sent the Rocks skipper to the stands. Without any video footage it is unlikely the club will appeal over the decision.
Keaton Wood came on for Walsh on 66 minutes to help the ten men defend. George Nicholas received the ball square from the right but directed his shot wide. Smith was fouled on the run on the right and Jack Humphrey went into the book. Leigh's free-kick saw Casey get a header down but the ball was cleared off the line on 70 minutes.
Tuck sprang on the attack with a speedy run but curled his strike wide on 73 minutes. Ward-Cochrane got beyond the defender before smashing it over the bar when it looked easier to commit Tangara into a save. Lethbridge won a free-kick as Dwight Pascal went into the book with a challenge on the left as sparks flew between the teams.
Cook went to ground holding his back and with Rocks in attack the referee stopped play while he received treatment. Bognor held on as the referee blew for full-time after four additional minutes. This could prove to be a crucial win in the fight to reach the play-offs and now the Rocks visit Corinthian Casuals on Tuesday (7.45pm).
Rocks: Tangara, Whyte, Crane, Tuck, Casey, Cook, Walsh (Wood 66), T Leigh (Mendoza 90), Smith, Flannigan (Kavanagh 73), Lethbridge. Subs not Used: Hopkinson, Wakley.