First-half goals from Guro Reiten and captain Magdalena Eriksson gave the Blues a win that moved them five points clear of second-placed Manchester United.
Later in the day, United scored a stoppage-time winner against 10-woman Manchester City to take the title fight down to the final day.
The Blues have reeled in previous leaders United and Marc Skinner’s side knew only a first WSL derby victory against their city rivals would keep their fight alive.
Reiten put Chelsea ahead with a superb half-volley and Eriksson poked home a second on what was her final home game for the club.
Chelsea were given a scare when Arsenal were awarded a penalty in the second half but their captain Katie McCabe dragged it wide from the spot.
Blues manager Emma Hayes said: "We were superb first half we really were, the number of chances, the way we controlled the game.
"Arsenal showed their quality in the second half but thanks [Katie] McCabe for making it less interesting.”