Arsenal topped the series for a couple of hours, but during the evening Chelsea regained the place as number one after defeating Reading with a full 5-0 at home.
The guests were never allowed into the match, where Chelsea in the last half bombed in three goals in a row, two of which came from forward Samatha Kerr.
In extra time, Bethany England poked in 5-0 on penalties.
The team captain, Swedish national team player Magdalena Eriksson, played from the start, just like the flawless goalkeeper Zecira Musovic.
Jonna Andersson sat on the bench for most of the match but was replaced with just over 10 minutes left to play.
Chelsea now have 44 points from 18 games played.
Arsenal are second, one point behind.