Arsenal came back from two goals behind to win 3-2 at second in the table Chelsea, as Jennifer Beattie's treble sealed a stunning comeback.
The defending champions moved up to fourth with the win, but have six games in hand over leaders Sunderland.
Doncaster Belles recovered from defeat in the cup last week with a 2-0 win over Bristol Academy.
Leeds Carnegie thrashed Blackburn Rovers 5-0 in the League Cup quarter final to set up a tie against Chelsea.
Women's Premier League
Chelsea 2-3 Arsenal
Former Arsenal players Lianne Sanderson and Leanne Champ gave the Gunners an early battering with a goal apiece in the first eight minutes.
A reinvigorated Arsenal came out after half time, and Beattie started the fightback with her first goal in the 49th minute.
The Scotland international then levelled the scores in the 70th minute and ensured her team would maintain their 100% record with a dramatic last-minute winner.
Watford 2-2 Birmingham City
England Under-19 international Isobel Christiansen made a great start to her Birmingham career with both of their goals.
The new signing - who only joined from Everton two days ago - opened the scoring in the 65th minute.
Holly Miles and Sam Pittock scored to put the Hornets in front, but Christiansen sealed her stunning debut with a stoppage time equaliser.
Doncaster Rovers Belles 2-0 Bristol Academy
A well taken 10th-minute Emma Johnson goal and an 84th-minute header by Vicky Exley gave the Belles their first home win of the season.
The result piled more misery on Bristol, who are anchored to the bottom of the table with just three points from nine games.
Nottingham Forest 1-1 Millwall Lionesses
Forest missed several early chances and paid the price when Lindsay Morgan shot the Lionesses in front after 27 minutes.
The home side hit back in the 66th minute to deservedly equalise through a Reanne Thomas header, but despite late pressure were unable to force a victory.
Women's Premier League Cup
Leeds Carnegie 5-0 Blackburn Rovers
Ellen White and Sue Smith both bagged braces as Leeds put themselves within 90 minutes of a place in the final.
White opened the scoring in the 26th minute, and two quickly taken Smith goals just before the interval put the home side well in control.
Carla Cantrell hit her seventh goal of the season seven minutes after the restart, and White took her tally to eight with a strike nine minutes from time.
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