Chelsea's lead at the Women's Super League summit was cut to six points after West Ham ended the Blues' season-long winning streak at Kingsmeadow in thrilling fashion.
Sonia Bompastor's side looked to be cruising to victory when Maika Hamano's volley and Aggie Beever-Jones' delicate finish put them two up after 21 minutes.
But Shekiera Martinez turned the game on its head, halving the lead just before the interval and reappearing in stoppage time to make it 2-2.
Only two other sides have denied the reigning champions maximum points this term, but the Hammers are the first to do so on Chelsea turf.
Second-placed Arsenal took advantage as Beth Mead struck twice in a 4-0 hammering of bottom side Crystal Palace.
The England forward opened the scoring with a 17th-minute volley and popped up again in stoppage time to grab another. Prior to that Alessia Russo had scored her side's second, while Palace skipper Allyson Swaby inadvertently turned Chloe Kelly's cross over her own line.
Manchester United also inched closer to locking down their Champions League spot next season with a 2-0 home win against Everton.
Visiting keeper Courtney Brosnan was culpable for the opener, with Dominique Janssen swooping in with the finish in the 22nd minute.
Grace Clinton added the second in the opening moments of the second half, with Everton managing nothing in response having seen their best effort ruled out early on for handball.
Fourth-placed Manchester City bounced back from their midweek Champions League exit at the hands of Chelsea with a 2-1 win at Brighton.
Kerstin Casparij appeared to have won it for the visitors with a first-half effort from close range before the sides traded goals in a flurry of late activity. Substitute Vivianne Miedema made it safe first but Charlize Rule hit back in a frantic finish.
Second-bottom Aston Villa bounced back from five straight defeats in all competitions to snatch a late 2-1 win at Liverpool, extending their gap over Palace to four points in the process.
After a goalless first half the Reds went ahead through Marie Hobinger's penalty, but Kirsty Hanson was on hand to restore parity with a smooth run and finish.
That looked enough to secure a good point for Villa but it got even better in the closing stages, Ebony Salmon firing in a cross that Liverpool substitute Jenna Clark deflected in.
Tottenham halted a run of five straight defeats with a 1-1 draw at Leicester. An own goal from Josefine Rybrink had put Spurs in trouble but they banked a first point since January 26 when Drew Spence levelled just after the hour mark.
PA
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