Sam Baldock’s clinical second-half double strike sent Barnsley spiralling to defeat and Brighton back to the top of the Championship.
The Seagulls looked every inch automatic promotion certainties during a hugely impressive performance in that second period.
Both sides created a number of chances during a goalless first period at sun-drenched Oakwell.
Ryan Kent’s early free-kick was deflected narrowly over the top, while Adam Armstrong went close with a lofted effort that drifted wide.
The Seagulls probably ought to have broken the deadlock after 20 minutes when Jamie Murphy dived in to meet Bruno’s cross, only to head woefully over the top.
Brighton bossed the latter stages of the opening 45 minutes with Anthony Knockaert, Baldock and Glenn Murray all going close.
The Reds created the first opportunity after the restart, with marauding midfielder Matty James seeing a thumping strike bravely blocked by Albion centre-back Lewis Dunk.
It was Brighton who went in front after 53 minutes.
A classy strike it was too, as Baldock met Knockaert’s through-ball before slamming a half-volley past Adam Davies from 20 yards.
The same combination of players combined for the Seagulls’ second goal in the 68th minute.
This time Knockaert twisted and turned in the Reds box before crossing for Baldock, who side-footed neatly past Davis this time.
Barnsley (4-4-2): Davies; Yiadom, MacDonald, Roberts, Jones; Watkins, Moncur (Mowatt, 80), James, Kent (Williams, 80); Armstrong, Bradshaw (Hammill, 63).
Subs not used: Townsend, Elder, Jackson, Lee.
Brighton (4-4-2): Stockdale; Bruno, Dunk, Duffy, Pocognoli; Knockaert (Tomori, 90), Stephens, Sidwell, Murphy; Murray (Akpom, 88), Baldock.
Subs not used: Walton, March, Hemed, Kayal, Hunemeier.
Referee: David Coote (Nottinghamshire).