The Republic of Ireland international left Lancashire for Sussex in August, having signed off with three own goals and a red card in his final two league games, and he scored again past Rovers goalkeeper Jason Steele – this one actually helping rather than hindering his current club.
Dale Stephens’ 61st-minute volley doubled the advantage and though Sam Gallagher swiftly pulled one back, substitute Glenn Murray coolly clipped in a third, after ex-Brighton defender Gordon Greer had been dismissed, meaning Gallagher’s second in stoppage time could not prevent the Seagulls moving ahead of Newcastle at the summit.
Duffy had developed his habit for scoring against Blackburn when he was still on their books and, back then, his manager Owen Coyle was querying the player’s mentality ahead of a saga that eventually saw Rovers cashing in to the tune of £4.2million.
Coyle’s view was that, with Duffy’s deal running down next summer, Rovers had little choice but to recoup something – and after selling central-defensive partner Grant Hanley too, former Brighton captain Greer was brought in as a replacement.
The 35-year-old was well placed to cut out Sebastien Pocognoli’s left-wing cross but, from the resulting corner, Blackburn’s old boy would beat the former Seagulls skipper in the air.
Oliver Norwood’s corner was delivered to the back post and Duffy jostled himself in front of Greer to nod downwards, with the bounce taking the ball beyond Steele’s left hand.
The centre-back celebrated the opener in normal fashion and there was no response in the direction of the fans who had jeered and chanted about him in the opening exchanges.
Though Duffy’s header came just 15 minutes in it left the hosts with a mountain to climb given Chris Hughton’s side had not conceded in five of their previous six away games.
Coyle’s men were creating chances – David Stockdale saving from Danny Graham and Ben Marshall – yet the visitors looked dangerous on the break through the dangerous Anthony Knockaert, while striker Baldock was wasteful on a couple of occasions from the edge of the area.
Stephens was not so profligate when the ball dropped to him in the area just after the hour mark as he steered a brilliant volley into the corner after another Norwood set-piece had been looped into the air by Darragh Lenihan’s header.
At that point, the visitors probably felt they had killed the game off but Blackburn found a way back five minutes later when Gallagher pounced for his eighth of the season after Derrick Williams’ initial attempt was blocked by Duffy.
Yet two yellow cards in 13 minutes for Greer, the second for upending Murray from behind, demoralised Blackburn again, with Murray then making it 3-1 as he dinked over Steele after Lewis Dunk’s original effort was saved.
Gallagher would make it nervy in the closing moments with a stoppage-time second as he out-paced Duffy, though Brighton would hang on to leave Hughton’s side sitting top.