Despite going in to the game top of Group Three with a 100% record, their fate is out of their own hands after goals from Jess Clarke and Rachel Corsie gave the visitors all three points.
In what was a scrappy game, both sides failed to find their passing rhythms early on. Potter fired a free-kick wide just six minutes in, but with 11 minutes on the clock Blues could have gone ahead.
From the right-wing, Karen Carney whipped a ball into the box which was cleared back in to her path. This time her cross picked out Hannah Keryakoplis, but the Welsh striker nodded over from six yards out – failing to get underneath the ball whilst at full stretch.
It took until the half-hour mark for Notts County to respond with an effort of their own, and Spencer had to be alert to tip over an effort from former Blues star Dunia Susi.
Both sides were pressing the opposition defences at every opportunity and that created gaps in the centre of the park – when Allen exploited one of these and skipped by two players she was eventually hauled down.
When Potter put in a corner from the right, it was cleared to the edge of the box where Allen was waiting, but her curling effort was gathered safely by England goalkeeper Carly Telford. Carter was next to try her luck from range, but was leaning back as she struck from 30 yards out following a cleared corner.
Four minutes before the break, Blues felt they should have had a penalty. Carney whipped a corner in from the right-hand side which first fell to Keryakoplis. Her effort was blocked and as Blues appealed for a penalty the ball fell to Kerys Harrop who had a second effort which seemed to clearly strike a hand. However, referee Akil Howson was not convinced and waved away both appeals.
Meaghan Sargeant replaced Carter at half-time – the teenager had picked up a first-half knock – and after four minutes of the restart Melissa Lawley came on to replace Keryakoplis.
The substitute would provide Blues’ most potent attacking threat in the second half following her return from injury and, five minutes after the hour mark, she latched on to a deep free-kick from Carney but, on the stretch, could not trouble Telford.
With 69 minutes on the clock, the winger tried her luck again as she let fly from 30 yards, but Telford was able to scamper across her goal quick enough to deny Lawley what would have been a spectacular goal. A minute later Jade Moore nodded wide after getting on the end of Carney’s right-wing cross.
15 minutes were left on the clock when Notts County took a lead against the run of play. Emily Roberts was played in down the right by Susi and she played a perfect ball in to the feet of Clarke who prodded the ball over the onrushing Spencer to give the visitors a lead.
Blues pressed for the final minutes but were unable to create a clear opportunity to draw level and subsequently fell further behind in the third minute of stoppage time when Corsie stepped up to stroke home a free-kick from 25 yards into the bottom corner.
The visitors now top Group Three by one point and will secure top spot if they beat Yeovil Ladies on Saturday. Blues host Bristol Academy next Sunday and will know in advance if they have a chance of topping the group. If not, they can still book a semi-final space if they finish as best runners-up, but that would require a win against Bristol and Arsenal Ladies to drop points in their final two games.
Blues: Spencer; Weston, Mannion, Harrop, Carter (Sargeant, 46); Moore, Potter; Allen, Carney (c), Keryakoplis (Lawley, 49); Westwood.
Subs: Baggaley, Simpkins, Wellings, Torkildsen, Haines.
Notts County: Telford, Susi, Hoyle, Bradley, Clarke, Scott, Crosie, Walton, Turner, Brogan (Roberts, 65), Whelan (Friend, 61).
Subs: Draycott, Unitt, Haywood, O’Neill.