Sasuke first awaken his sharingan

Answer 1

actually it was when itachi killed the village and it dosent show u until about episode 135-142 but sasuke is chasing after itachi and basically losses control he obtains the first lvl of sharingan (u will notice that vs haku, he has two swirly balls next to the actual inner pupil) but against itachi he gets the first swirly balll thing but then after like five seconds of maintaining itachi is so proud but he has to leave the village, then sasuke passes out, wakes up in hospital badabing badaboom btw he cant activate it untial zabuza because he was practically unconsious when he got it so he thought he hadnt achieved it yet

******************NEW ANSWER *******************

Sasuke first awakens the first level of the Sharingan when he was 7, before the start of the original Naruto series, when Itachi massacred the Uchiha clan. For most of the episodes in the original series, Sasuke doesn't use it because Sasuke forgotten he had activated it as he was traumatised by the incident. He reactivated it during the Land of the Waves arc while fighting Haku, where his right eye has two tomoe in it. By the time he fights Rock Lee in the Chunin Exams, both his left and right eyes had two tomoe. Midway during his battle against Naruto at the Valley of the End before the end of the original series, it has three tomoe in each eye. His mangekyo sharingan was obtained in Shippuden after Itachi died and his eternal mangekyo sharingan was obtained after implanting Itachi's eyes into his own sockets.