On a general note, I would use BS before Ancestral if I can suspect opponents Mis-D.
BS could allow you to find FoW or Mis-D ( you have 7 of them in your deck ) to protect Ancestral in a better way.
Talking about your specific example, opponent's game/hand/board situation was SO strong that you could have won ONLY with the maximum amount of cards seen in a single turn HOPING that he didn't keep some 0cc-counters ready to be played.
BS+Ancestral are 4 cards seen if you cannot optimize a fetch or a tutor.
Ancestral + BS are, instead 6, and this specific terrific game situation forced you to play in a less conservative, rewarding you with a good win.
Brainstorm
Merchant Scroll
Polluted Delta
Mana Drain
Mana Crypt
Black Lotus
Tolarian Academy
Flooded Strand
You could have played BS+Fetch+Ancestral in order to see 6 cards and optimize BS anyway, but you would have loss the ability to play and win through T.Academy.
I would have played exactly as you, but expecting to lose the game because that specific lucky pile of spells would never represent anymore in real life 
