Braces apiece for Dutch forward Vivianne Miedema and England star Jordan Nobbs came after Kim Little had broken the deadlock midway through the first half from the penalty spot.
The prolific Gunners, who are looking to claim their first WSL title since 2012, have now scored 21 times in their four league games this season, bagging 33 in all competitions.
This was the first time that Chelsea had tasted defeat after 25 games unbeaten.
Arsenal weren't the only big winners in WSL on Sunday, as Manchester City hit West Ham for seven in their game. England captain Steph Houghton marked her 100th WSL game with one late on, while Nikita Parris and Georgia Stanway both hit doubles.
Caroline Weir opened the scoring after just two minutes, with Tessa Wullaert scoring the seventh for City in the closing stages. Esmee de Graaf netted one in consolation for West Ham.
Birmingham returned to winning ways this weekend after dropping their first points of the season last week. The Blues were narrow 1-0 victors away at Bristol City, courtesy of a solitary screamer from Aoife Mannion 15 minutes from time.
Birmingham remain level on points with Arsenal at the top as a result of the victory, although have played a game more and possess a much inferior goal difference.
Elsewhere, manger-less Liverpool were slim victors over bottom club Yeovil, who still remain without a point after four straight losses at the start of the season.
It looked as though Yeovil might have done enough for a draw after Annie Heatherson cancelled out Liverpool's openerm scored by Kirsty Linnett in the first half. But with only three minutes of the 90 remaining, Jess Clarke popped up with the last-ditch winner for the Reds.
Three points for the Reds! pic.twitter.com/33VQnNNLtA— Liverpool FC Women (@LiverpoolFCW) October 14, 2018
Neither Everton nor Brighton had won prior to this weekend's clash and that didn't change after the teams scored six goals between them to draw 3-3.
Somehow, neither side had actually scored a WSL goal in seven combined games before this one. But Everton found themselves 3-1 up with just 20 minutes to go after Chloe Kelly netted what looked like a decisive goal, only for two quick-fire goals from Ellie Brazil to tie the contest.
In the second tier Women's Championship, a rampant Manchester United returned to winning ways after being held to a surprising 0-0 draw by Durham in their last game. The new club won 3-0 against Charlton, taking their goal tally for the league campaign to 23 in five games.
They are still also yet to concede a goal and remain hot favourites for the title and promotion.