Yasuo is at his most vulnerable after casting his Windwall since the cooldown is upwards of 26 seconds long.
Yasuo is also vulnerable after missing his 3rd Q, his tornado.
In an open map where many of the towers have already collapsed, try to avoid running back to your minions since they allow Yasuo to catch up to you.
Some counter champions against Yasuo: Jax, Fiora, Riven.
Jax's Counterstrike dodges Yasuo's Qs and can heavily punish Yasuo if he misses his tornado, knowing that his Windwall doesn't stop melee basic attacks and that it takes about 3-6 seconds to gain another tornado, Jax just alls in and landterns his face.
Fiora can actually use Yasuo's EQ against his if she times her Riposte at the same time Yasuo EQs and will end up stunning Yasuo instead. Just like Jax, Windwall is useless against Fiora.
Riven is the antithesis of Yasuo, their kits are direct counters of eachother. Riven's abilities are free to cast whereas Yasuo needs at least 1 target or need to meet some kind of condition to apply its effect. Yasuo's Windwall can block Riven's Wind Slash and Riven's Ki Burst can stop Yasuo from activating his ulti if he wants to EQ. Rivens stats are based off pure attack damage and her ulti grants more AD whereas Yasuo's passive grants 2x critical strike.
I can go on forever, but as Riven you'd want to use Ki Strike at the same moment you think Yasuo would use EQ, just like Fiora would. Riven's free to cast abilities allow her to reposition herself away from Yasuo's tornado or chase a Yasuo that is running away, since if a Yasuo is running away, he only has his allied minions to help him, which he cannot dash through.