Albion battled to their third home win in a row to keep their survival hopes very much alive.
The Seagulls bounced back from the midweek defeat at relegation rivals Stoke to add to earlier Withdean victories against Wolves and Millwall.
Resilient Rotherham's resistance was broken in the second half with an unlucky own goal by pint-sized leftback Paul Hurst.
Bobby Zamora added his 11th of the campaign 11 minutes later to boost Steve Coppell's side ahead of a tough run of fixtures.
A crowd of 6,468, braving wind and rain, had little to get excited about in a turgid first half.
Richard Carpenter had a volley ruled out by a linesman because the ball had gone out of play when Zamora crossed to him.
The outstanding Danny Cullip and Anthony Rougier both headed wide, while at the other end Dave Beasant made a diving stop from a shot by former Seagulls loan target Curtis Woodhouse.
The breakthrough Albion craved arrived in freak fashion on 56 minutes.
Rougier's close range stab was smothered by keeper Mike Pollitt, but the ball ricocheted in off Hurst, facing his own goal.
The unmarked Zamora cemented the advantage on 67 minutes when he converted Carpenter's corner at the far post.
Rotherham rallied in the closing stages as they threatened to set up an anxious finish.
The stretching Beasant made a brilliant one-handed stop on the line from a shot on the turn by the Millers' captain Martin McIntosh.
Former Seagull Richard Barker also headed against the bar from a free-kick by fellow sub Darren Garner, but it was too little too late for the Yorkshiremen as Beasant celebrated consecutive clean sheets at home.
Victory moves the Seagulls clear of the drop zone again after Stoke could only draw at Ipswich.
Albion and Stoke have the same points but lead the Potters on goal difference.
Sheffield Wednesday's 1-1 draw at Leicester gives Albion a two point lead over the Owls. Grimsby did not play.
Gary Hart is available again after a four-match ban for next Saturday's visit by Nottingham Forest.
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