Scotland’s Kim Little scored a brace after Vivianne Miedema’s opening goal and Katie McCabe and Leah Williamson were also on target as Jonas Eidevall’s side rioted at Meadow Park to beat rivals Tottenham at the goal difference.
Fran Kirby opened the scoring in under two minutes with his 50th Super League goal, and Chelsea were leading three at halftime.
Pernille Harder had a brilliant solo run to double the lead before Sam Kerr scored a third.
Alessia Russo gave United hope with a deflected shot shortly after half-time, but goals from Kerr, Drew Spence and Jessie Fleming made Chelsea’s day emphatically.
After being stunned by Arsenal in their opener, it was a performance to show Emma Hayes’ side are firmly back on track.
Tottenham maintained their perfect start with a 1-0 win over Reading.
They had to wait until the 85th minute to make the breakthrough, with Jessica Naz grabbing the goal.
Aston Villa came out on top by the same score at Brighton, with Emily Gielnik putting in a fine finish three minutes after the break.
West Ham claimed their first win of the season on a high note with a 4-0 victory over Leicester.
Australian debutante Tameka Yallop opened the scoring in the 26th minute, and Claudia Walker added her first goal for the club 12 minutes later.
Ashleigh Plumptre’s unsuccessful home goal made it three just before half-time and Yallop scored his second goal late in the second half.
Additional reporting by the Press Association.