The Seagulls have yet to concede a goal this term and first half goals from Anthony Knockaert and Glenn Murray put them on their way before a crowd of 25,128 at the Amex Stadium.
Israeli international striker Tomer Hemed completed the scoring with a 58th minute penalty to leave Rotherham still searching for their first win under manager Alan Stubbs.
Brighton boss Chris Hughton gave a debut to Finland international goalkeeper Niki Maenpaa with David Stockdale nursing a shin injury, and Maenpaa was relieved to see a right-footed shot from skipper Stephen Kelly fly over.
But Albion took a firm foothold in the game by scoring twice in the space of three minutes through Knockaert and Murray.
Frenchman Knockaert broke the deadlock in the 23rd minute by firing home from the edge of the area after being set up by Bong. Keeper Lee Camp got a hand on the ball but could not keep it out as Knockaert scored his seventh goal in 13 appearances at the Amex.
Liam Rosenior later delivered the perfect cross for Murray to hit his third goal of the season with a well-taken shot on the turn at the far post.
Oliver Norwood and Jamie Murphy both put shots wide for the dominant Seagulls before the interval, while, at the other end, Maenpaa did not have a shot to save.
Hemed struck from the penalty spot to make it 3-0 on 58 minutes, sending Camp the wrong was after Murray was brought down by Stephen Kelly.
Hemed headed wide from a cross by midfielder Norwood as the one-sided nature of the contest continued.
Rotherham produced very little by way of attacking threat, but Maenpaa did well to save a goalbound shot from Ward, before turning a fierce drive from Will Vaulks round the post.
The Millers had their best spell late in the game and Maenpaa was put under pressure by a poor back pass from Norwood.
Brighton: Maenpaa, Rosenior, Saltor, Dunk, Bong, Knockaert (LuaLua 69), Stephens, Norwood, Murphy, Hemed, Murray (Baldock 69). Unused substitutes: Kayal, Skalak, Sidwell, Ankergren, White.
Rotherham: Camp, Fisher (Thorpe 89), Kelly, Kelvin Wilson, Ball, Mattock, Forde (Allan 46), Vaulks, Smallwood, Taylor, Ward. Unused substitutes: Wood, Price, Yates, Warren.
Referee: S Hooper (Wiltshire).