This is a discussion on I know the odds, want the why? within the online poker forums, in the Tournament Poker section; Why is it that having an :as::2s4: a 18.79% of winning higher than if I had :ah::2h: 18.69% of winning against :8h4::8s: with a flop
Its because, if you have Ah2h, then Th9h will give you a better two pair than his (counterfeit), and a flush. If you have As2s however, then Ts4s will only give you a flush. So with As2s you have just as many ways to make a flush, but you have one more way to win on a counterfeit. This is admittedly very nerdy and took me a while to figure out
If 2 spades come then you'll be able to make a flush but it's highly unlikely. That's why the percentage is low. If an ace comes then you will win. The percentage is higher due to the spade being on the flop.