The London club replaced Manchester United at the summit as Emma Hayes' defending champions won 3-2 at Tottenham.
Jess Carter headed the visitors into an early lead, which was cancelled out by a strike from former Chelsea forward Bethany England in the 16th minute.
James restored Chelsea's advantage just before the half-hour mark, picking up the ball on the right flank and bursting past three defenders before firing into the bottom corner.
Guro Reiten added a third for Hayes' side on 64 minutes, latching on to a Kerr flick-on to race clear and beat keeper Tinja-Riikka Korpela.
Nikola Karczewska reducing the deficit with two minutes of normal time remaining but Spurs were unable to avoid a sixth successive league defeat.
"It was a scrappy game," Chelsea coach Emma Hayes said.
"First half we didn't create enough depth to have the control we wanted, at least in the deeper spaces. We played ourselves into trouble.
"But this is a tough league. Anybody who thinks it's going to be near-perfect performances, it's not. It's going to be a grind until the end."
Coupled with Manchester United's 0-0 draw at home to fifth-placed Everton, the result meant Kerr's Chelsea moved two points clear at the top of the table.
Lucia Garcia and Alessia Russo - playing for the first time since United rejected a world-record bid for her from Arsenal on transfer deadline day - saw efforts hit the Toffees' goal frame in the first half, and Ella Toone then struck a post after the break.
Arsenal's Steph Catley and Caitlin Foord were unable to get the better of their Matildas teammate Mackenzie Arnold, who kept a clean sheet for West Ham as the two London sides shared a goalless draw.
The result took Arsenal back above Hayley Raso's Manchester City into third place. They are five points behind Chelsea and three behind United, with a game in hand over both.
Liverpool rose to eighth, pushing Tottenham down to ninth, with a 2-0 home win over 11th-placed Reading.
- with PA
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