This clash might have been played out in monsoon-like conditions, but West Ham were home and dry by the interval, thanks to the goals from Bobby Zamora, Marlon Harewood and Hayden Mullins.
Gillingham came into this contest in 23rd spot, just one place above an all but tailed-off Rotherham United and while this game followed the form book, the Kentish strugglers might have caused an early shock against the high-flying Hammers.
Firstly, the unmarked Mamady Sidibe wastefully headed across the face of goal before player-manager Andy Hessenthaler burst into the box and forced Stephen Bywater into a low save.
But that was about as good as it was to get for the Gills.
For, on 17 minutes, Harewood sent strike partner Zamora clear and the former Brighton striker outsmarted the retreating Nyron Nosworthy, before gleefully claiming his fourth goal of the campaign with a low 15-yarder which flew beyond the outstretched palm of the diving Jason Brown.
And eight-minutes later, the over-lapping Zamora returned the compliment when he raced on to Matthew Etherington's throughball and crossed to the near post where Harewood slid home a rising six-yarder, to take his season's tally to half-a-dozen.
Things got steadily worse for ground-down Gillingham as Nosworthy was booked for felling the escaping Zamora, and then injured striker Patrick Agyemang was replaced by Darren Byfield.
To compound their misery, the hungry Hammers were not finished in the goals department, either and when Etherington's 39th-minute corner was only half-cleared to Zamora, his fierce, angled shot was met by the stooping Mullins who headed home his first league goal for West Ham at the far post.
In first-half injury time, Byfield gave Gillingham just a glimmer of hope when he met Nosworthy's deep cross with a looping ten-yard header that caught out the stranded Bywater to make it 3-1 at the interval.
Nearly a year ago, Hammers notoriously squandered a 3-0 lead to lose 3-4 against West Bromwich Albion, and as West Ham somehow found themselves under increasing pressure after the break, an air of apprehension began to surface around Upton Park.
Certainly, when Danny Spiller's 63rd-minute thunderbolt scorched through the torrential East End rain on to Bywater's left-hand post, West Ham knew that their stranglehold on the game had finally loosened.
But Gillingham simply did not have enough firepower to chip any further into the two-goal deficit and, having used all three substitutes, their uphill task then took on Everest-like proportions when they were reduced to ten men after the unfortunate Byfield was stretchered away following a heavy collision with an advertising board.