The Hammers had to defend their lead desperately at times, with Amber Tysiak, Sáez and second half substitute Shannon Cooke under what felt like a siege of Everton crosses.
Seraina Piubel added some much-needed energy to the forward line in the second half. The forward raced away from several markers before laying the ball off to Shelina Zadorsky to strike, but her effort from outside the area flew over.
The home side eventually equalised, and it came with a wicked slice of fortune. A counter attack from the Blues saw Melissa Lawley find space wide on the right, with her cross flicking up off Sáez and over a stranded Szemik to level proceedings.
Towards the end of the contest, Dagný Brynjarsdóttir headed a ball into the path of Cooke, who saw her diving header courageous blocked in front of goal.
West Ham United: Szemik, Tysiak, Sáez, Zadorsky, Denton, Gorry ©, Siren (Brynjarsdóttir 73), Mengwen (Cooke 46), Harries (Piubel 59), Ueki, Asseyi (Smith 83)
Subs: M.Walsh (GK), Bergman Lundin, Paví, Houssein
Goal: Denton 10
Booked: Asseyi, Gorry, Cooke
Everton: Brosnan, Hayashi, Wheeler, Vanhaevermaet, Bissell (Sarri 55), Hope, H. Payne (T. Payne 55), Finnigan ©, S. Holmgaard, Snoeijs, Olesen (Lawley 66)
Subs: Ramsey (GK), Foster (GK), Hobson, Settle, Jones, Thomas
Goal: Sáez OG 73
Referee: Richie Watkin