English champion Rebecca Hudson celebrated her 23rd birthday by knocking out former Welsh champion Brewerton by 4 & 3.
Now Hudson meets her Curtis Cup colleague and Yorkshire compatriot Emma Duggleby on Friday morning for a place in the quarter-finals.
First 30-year-old Duggleby - runner-up for the past two years - needed three extra holes to get past Scotland's British girls champion Clare Queen.
Shock
Then the Malton and Norton club player was taken to the last in the afternoon by Germany's Miriam Hiller but Duggleby survived by the skin of her teeth.
Jo Pritchard caused one of the surprises of the round when she eliminated her Welsh international team-mate Sarah Jones, a member of the Great Britain and Ireland squad, by 3 & 2.
Pritchard was four under par when the match finished.
In-form Scottish champion Heather Stirling was another shock casualty, going down 6 & 5 to Wales' Anna Highgate, who was four under par for the match despite suffering a lost ball.
Irish title holder Alison Coffey, who led the qualifiers on Wednesday, made smooth progress into round three.
Ladies British Open Amateur Golf Championship, Ashburnham, West Wales second round: D Simon (Ger) bt K Knowles (Worplesdon) 2 & 1, M Prieto (Spa) bt M Campomanes (Spa) 21st, P Fraysse (Fra) bt E Pilgrim (St Pierre) 2 & 1, R Fry (Aus) bt S Doring (Ger) 3 & 2, R Hudson (Wheatley) bt B Brewerton (Abergele) 4 & 3, E Duggleby (Malton & Norton) bt M Hiller (Ger) 2 holes, M Gillen (Deaverstown) bt R Prout (Betchworth Park) 3 & 2, A Highgate (Cottrell Park) bt H Stirling (Bridge of Allan) 6 & 5, A Coffey (Warrenpoint) bt L Holm Sorensen (Den) 6 & 5, V Uwland (Aus) bt K Evans (Conwy) 2 & 1, J Pritchard (Tredegar Park) bt S Jones (Pennard) 3 & 2, R Quiazon (USA) bt L Mar (Spa) 3 & 2, V Costa (Ita) bt M Scalabre (Fra) 1 hole, L Wright (Aus) bt C Coughlan (Cork) 3 & 2, S Heath (Shifnal) bt A Knutsson (Swe) 1 hole, L Wessberg (Swe) bt F Schaeffer (Fra) 5 & 3.