Chelsea received off to a flying commence when Kerr built the most of some shoddy defending from United in the second moment to participate in in Kirby, who tapped in from close assortment.
Pernille Harder doubled their advantage with a good solo operate and dink in the 24th minute.
The site visitors piled extra misery on United 4 minutes before the interval as Kerr and Kirby reversed roles for the Australian worldwide to stab property a third.
United improved right after the split and pulled just one back via substitute Alessia Russo in the 48th moment.
But Chelsea restored their three-intention guide practically promptly when Kerr drove residence a cross from the right. Replays, even so, suggested the 28-year-aged may have been lucky not to be flagged for offside.
Substitutes Drew Pence and Jessie Fleming grabbed a objective every in advance of entire-time, leaving both of those sides on six points from their opening 3 games.
Further reporting by Reuters.