Goals by in-form striker Scott Dobie and prolific dead ball specialist Neil Clement came in the space of four first-half minutes and condemned inconsistent Gillingham to their third home defeat of the season already.
However, Gillingham began well, and gave Albion plenty of problems early on.
But Albion took a complete stranglehold on the game, the moment Dobie fired them in front with his third goal in three games and Albion never looked back after that.
Victories over Stoke and Millwall had maintained the Baggies' 100 per cent home record, and this was their third win on the road, and their fourth League success over Gillingham in five meetings.
Boss Gary Megson believes that going top so early in the season does not mean too much, but he will be pleased with the way his players performed against a side who looked way below par, and who were chasing the game by the half-hour mark.
Dobie and fellow striker Rob Hulse had enjoyed little success early on against Chris Hope and Ian Cox, until Phil Gilchrist 's long 30-yard pass caught the Gillingham defence napping.
The ball sailed over the last line leaving Dobie to run on and calmly convert past Jason Brown.
Brown was then given no chance to keep out Clement's curling 20-yard free kick repeating the goal he scored three seasons ago on the same ground.
Gills boss Andy Hessenthaler, who believes Albion are the best side in Division One and will go on to win the title, is urging his team to be more consistent in their fourth season in Division One.
A point at Rotherham and defeat at Walsall have followed a great win at West Ham, and now the Kent club face a two-week break due to next week's game against Sunderland being called off due to international commitments.
Hessenthaler means to use the break to mix rest with plenty of work on the training ground but his team looked distinctly out of sorts and the second half was merely a damage-limitation exercise although Albion only created one clear-cut chance themselves through substitute Lee Hughes.