Best recently defeated Zero twice in the Ultimate Battle Event as in the links below:-
https://www.youtube.com/watch?v=KmWxrvUHZiY&t=1h30m10s
Here are some of the points from Best's gameplay which I think are crucial:-
1. Put in double cannons at the 1st natural/ choke point when lings are scouted to prevent a possible ling all-in.
2. Critical number of corsairs - about 3, to snipe Overlords and to slow Zerg's production. Too many corsairs might not be effective as the Zerg will then train Scourges in combination with mutas or hydras.
3. Mass gateways (about 8 gateways built) before the 11th minute mark to ramp up gateway units production.
4. Unit composition. Often, the dragoons are neglected in favour of more zealots in PvZ, and only trained to counter mutas from sniping HTs. However, dragoons do provide cover for HTs as they have a ranged attack and they can also provide meat shields to the HTs when positioned ahead of the HT in the firing line.
Note that dragoons do not necessarily counter hydras but their range attack coupled with a mix of zealots and storms will counter the hydra-bust as shown by Best in the links above.
What do you guys think?