Paul Kitson made a sensational comeback as Albion turned the table on its head.
The former West Ham marksman headed his first goal for the club on 77 minutes, just five minutes after replacing Graham Barrett.
It put Albion 2-0 ahead following Paul Brooker's sixth of the season on 16 minutes from a smartly taken indirect free-kick inside the box by Bobby Zamora.
The Seagulls rode their luck as Brooker headed off the line and Reading should have been awarded a penalty for a foul by Kerry Mayo on Nicky Forster.
Sub Jamie Cureton pulled a goal back from long range for the play-off chasing Royals on 84 minutes, but Steve Coppell's battlers held on for three priceless points in their survival bid.
Albion's only change was significant in more than ways than one. Zamora returned from a slight hamstring tear in place of ankle injury victim Dean Blackwell.
Coppell abandoned the system of three central defenders, employed since November, and went instead for an attacking 4-3-3 formation.
Barrett, back from Republic of Ireland duty, kept his place up front alongside Zamora and Hart, while Kitson was back on the bench.
Reading gave a debut to Burnley winger Little, signed on loan on transfer deadline day. Skipper Williams returned from a knee injury to partner Brighton-born Brown but Sidwell had to settle for a place among the substitutes and fellow former Albion loan signing Anthony Rougier did not make the squad.
Coppell's tactical tinkering was partly designed to combat Reading's system of flooding the midfield, with Forster alone through the middle.
Hart, beginning the game on the left wing, gave American keeper Hahnemann a comfortable save in the opening minute with a low drive from an acute angle.
Brown, who nearly signed for the Seagulls in December, went into the book with only four minutes on the clock for a tackle from behind on Zamora just inside Reading territory.
Albion looked the brighter side early on and they were rewarded after 16 minutes with a goal arriving from some sharp refereeing by Mark Cowburn and quick thinking from Zamora and Brooker.
The Blackpool official penalised Hahnemann for picking up a back pass from Murty.
The Seagulls were awarded an indirect free-kick in a central position ten yards out.
Zamora tried to get the ball off Hahnemann, the keeper threw it away but Brooker played it back to Zamora so he could take the free-kick rapidly.
Zamora played it square for Brooker to slot past the bemused Hahnemann.
Television replays showed that Cowburn made the correct decision.
It took Reading until the 26th minute to mount a decent effort on Albions' goal.
Cullip, passed fit following a hamstring problem, could not clear a cross from Harper, but Forster fired over from close range.
Hart was cautioned two minutes later for a foul on Murty.
The onus was now very much on the home side to take the game to Albion, although that does not really suit Alan Pardew's style of play.
The Seagulls seemed pretty comfortable at the back as Reading, via three corners, enjoyed sporadic pressure. Forster spurned another opening for Reading with a shot straight at Beasant after an uncharacteristically loose pass by Ingimarsson.
Brooker became a hero for Albion at both ends of the pitch six minutes from the break when he nodded the unmarked Little's far post header from Harper's corner off the line.
It was a rare scare for the Seagulls, now playing much more on the break as Reading gathered momentum.
Carpenter had a volley headed away by Williams after combining with Zamora, then Hart just failed to reach a low centre from Rodger as he slid in at the back post.
A fine stop by the evergreen Beasant preserved Albion's lead on 43 minutes. He was drawn towards Forster and, as the Reading forward spun away to cross into the danger zone, Beasant recovered his ground to block Little's fierce resulting volley.
Mayo was a little fortunate not to concede a penalty in first half stoppage time when he appeared to bring down Forster just inside the right hand edge of the penalty area.
Albion bizarrely found themselves in the hands of a replacement referee from Brighton for the second half. Fourth official Clive Penton, from Woodingdean, took over from Cowburn, who picked up a calf injury.
Reading continued to press in the early stages of the second half but Albion held firm, with Cullip in dominant mood once more.
Reading made a change in midfield approaching the hour mark, Watson coming on for Newman.
Zamora blemished his polished first half performance with a booking shortly afterwards. He tried to beat Hahnemann with a shot after new ref Penton had blown for offside against the Albion ace.
Forster missed two more chances to level, skewing wide after cutting inside Cullip and then holding off Ingimarsson to shoot just the wrong side of the far post.
Coppell made a double substitution as Reading continued to press. Kitson came on for Barrett and Jones for Hart. Reading also made a substitution, frontman Cureton replaced midfielder Hughes.
It took Kitson five minutes to double Albion's advantage.
His header from Carpenter's free-kick was half blocked by Hahnemann but rolled over the line.
Cureton set up a grandstand finale six minutes from time with a spectactular 25 yarder which swerved over Beasant.
Albion (4-3-3): Beasant (gk) 7, Watson (rb) 7, Mayo (lb) 7, Cullip (cd) 8, Hart (lw) 7, Brooker (m) 8, Carpenter (m) 7, Ingimarsson (cd) 7, Zamora (f) 8, Barrett (rw) 7, Rodger (m) 7. Subs: Kitson for Barrett (withdrawn 72), Jones for Hart (withdrawn 72), Oatway for Rodger (withdrawn 79), Pethick, Packham.
Scorers: Brooker (16), Kitson (77).
Bookings: Hart (28) foul, Zamora (61) unsporting behaviour.
Reading: (4-5-1): Hahnemann, Murty, Shorey, Williams, Forster, Hughes, Harper, Little, Newman, Brown, Chadwick. Subs: Watson for Newman (withdrawn 59), Cureton for Hughes (withdrawn 72), Ashdown, Tyson for Chadwick (withdrawn 79) and Sidwell.
Scorer: Cureton (84)
Booking: Brown (4) foul.
Half-Time: Reading 0 Albion 1.
Attendance: 16,133.
Fan's View: Mike Duffell (Worthing).
Mike Duffell (Worthing)
I thought Brighton defended particularly well.
We should have used the width a bit more but that might have been down the formation we adopted.
Bobby Zamora held the ball up well and I was impressed with the amount of work Gary Hart got through.
The experience of Dave Beasant came into play time and again. You could see him calming people down when needed.
Was I pleased to see Kitson score? I'm pleased to see anyone in a Brighton shirt score but that goal has got to be good for his confidence.
Overall, a tremendous all round display.
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