"Sasuke's Taijutsu…!!" (サスケの体術…!!, Sasuke no Taijutsu…!!) is chapter 112 of the original Naruto manga.
Kakashi explains that, having seen Lee's fighting style before with his Sharingan, Sasuke has been training this last month to reproduce his speed. Lee knows from prior experience that speed is not enough to defeat Gaara, but Guy recognises that the speed must serve some other purpose. After he continues to be pummelled by Sasuke, Gaara retreats into a Shield of Sand, which he shaped into a sphere, to give himself time to prepare. Sasuke is unable to break through this defence with speed alone. Naruto, worried that Sasuke will be killed, races to the arena to try and stop the match. Kakashi promises that there was a good reason for why they were late.