Manchester United conceded their first goals of the season in a 3-1 loss at home to Chelsea that allowed Arsenal to go top of the Women's Super League on Sunday thanks to a 4-0 thrashing of bottom side Leicester City earlier in the day.
The Gunners lead on a perfect 18 points from their six games and are ahead of Chelsea on goal difference, while United slip to third spot on 15 points.
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Striker Sam Kerr scored on the hour mark after Millie Turner passed the ball straight to Chelsea's Sophie Ingle, who played in Australia international Kerr for a controlled finish to break the deadlock.
Minutes later Kerr turned provider, sliding the ball into the path of Lauren James, who scored with a first-time finish before Alessia Russo pulled one back for United to set up a grandstand finish.
However, rather than snatch an equaliser, United conceded a third as Erin Cuthbert fired home a deflected shot in stoppage time to wrap up the three points for the Blues.
Earlier in the day, Brighton & Hove Albion scored five goals but barely managed to hang on for 5-4 win away to West Ham United, with Viviane Asseyi grabbing two late goals for the home side.
Reading defender Emma Mukandi had a day to forget, scoring two own goals in eight minutes as her side lost 3-0 at home to Manchester City to leave them second from bottom in the table.
Liverpool's poor run of form continued with a fifth straight defeat as a Rachel Daly penalty just before the hour mark gave Aston Villa a 1-0 win over the newly-promoted side, whose only victory this season so far came in their opener against Chelsea.
Tottenham Hotspur's home game against Everton was postponed due to a waterlogged pitch.