Arne Slot’s side took the lead through Harvey Elliott’s early opener before Yasin Ayari equalised at the Amex Stadium.
Dominik Szoboszlai restored Liverpool’s advantage just before the interval, but Brighton staged a late fightback as Kaoru Mitoma levelled before Hinshelwood came off the bench to net with his first touch.
Liverpool have taken just one point from their three matches following the title-clinching rout of Tottenham on April 27.
The Reds have lost at Brighton and Chelsea and squandered a two-goal lead in a draw with Arsenal since their record-equalling 20th English crown was confirmed
They can now look forward to receiving the Premier League trophy in Sunday’s season finale against FA cup winners Crystal Palace at Anfield before an open-top bus parade through the city 24 hours later.
Slot had admitted that motivating the champions for the final two matches of the season was a tricky task and his fears were confirmed by this sloppy display.
Slot’s players had a celebratory trip to Dubai this week and only returned to training on Friday, while the Reds boss was seen partying in Ibiza for several days, as they soaked in a title victory secured in April.
“Did you see me on social media!” Slot said with a laugh in reply to a question about how focused he had been on the Brighton game.
After being given a guard of honour by Brighton’s players before kick-off, Liverpool initially showed signs of rebuking the doubters who claimed their minds were elswhere.
Ahead of his widely-expected move to Real Madrid when his contract expires in the close-season, Trent Alexander-Arnold was left on the bench for a second successive game.
Conor Bradley featured at right-back instead and showed why he is a contender to replace Alexander-Arnold with his role in Liverpool’s ninth minute opener.
When Mohamed Salah rolled a pass to Bradley, he shifted gears with a dynamic burst into the Brighton area before clipping a precise pass towards Elliott, who slotted home from close-range.
The goal meant Liverpool had scored in every away game of a league season for the first time in their history.
Bradley’s attacking runs had more than a touch of Alexander-Arnold about them, but his finishing wasn’t up to scratch when he took Federico Chiesa’s pass and fired wide from 10 yards.
Ayari grabbed Brighton’s eye-catching equaliser in the 32nd minute.
The Sweden midfielder eluded Bradley and drilled a fine low finish past Alisson Becker from the edge of the area after Brajan Gruda’s lofted pass prised open the Liverpool defence.
Liverpool regained the lead on the stroke of half-time when Szoboszlai caught out Brighton keeper Bart Verbruggen with a swerving strike from wide on the right flank that whistled into the top corner.
Szoboszlai’s bemused grin as he celebrated suggested the midfielder’s effort might have been a miscued cross rather than a shot.
Brighton went close twice at the start of the second half as Alisson clawed away Danny Welbeck’s free-kick and kept out Gruda’s 20-yard blast.
Salah was captaining Liverpool for the first time in the Premier League to mark his 300th appearance in the competition.
But the Egypt forward missed an open goal when he flicked Cody Gakpo’s cross wide from five yards.
It was a costly mistake from Salah as Brighton equalised in the 69th minute. Welbeck’s shot was pushed out by Alisson and Japan winger Mitoma hammered in the rebound.
Hinshelwood completed Brighton’s thrilling comeback in the 85th minute, the substitute slotting home from Matt O’Riley’s cross. (AFP)
