Really? Look at how beat down he was by Nnoitra before using Kendo which he also has yet to use. It was to the point where he was using cheap tactics like pretending to be dead which is very out of character for him. Granted it might be even worse now but we know he goes to extreme measures before going all out. In fact he did not resort to kendo against Ichigo and it resulted in a double KO.
I remember that he was hurt pretty badly by Noitra. I also remember that he had removed his eyepatch a fair way before he even got to that stage (the eyepatch was like him going serious, kendo was more of a last resort).
As damaged as he was in that fight, however, it still pails in comparison to his current state. Not only has be been beaten, had his guts crushed by the space vacuum thing, but it looks as though he can barely move in his current state. As far as I remember, this is the worst condition we've ever seen Kenpachi in. He's a guy who enjoys the fight, and will balance himself so that he's in state where he can enjoy the fight. The fact that he's been reduced to being sprawled on the ground suggests there's no more he can do, then. I find it very, very hard to believe that even now, he isn't being serious. If he does just hop back up, or worse yet, do that and then pull a bankai out of his ass, then I'll admit that I'm wrong, but that would be terrible writing on Kubo's part.
Also, having awakened his zanpakto, I'm not sure the whole 'Kendo is my uber move' thing applies anymore. It looks like Kenny's going to need saving on this one (good thing Ichigo turned up).
@Zerogodlike: Yeah I get what you're saying, Kenpachi lose due to speed disadvantage, but Kenpachi has yet to take off his eye patch and show his Bankai. And as we know with Kubo and Kenpachi once he does that his power then should dwarf his power now imo, but it'll still take Sasuke a few good hits to take down Kenpachi due to his incredible durability.
@DevilMayhem666: Aye, I understand Yama is quite the badass XD but you do have to admit that Sasuke does not have or has not shown the sheer durability and endurance of Kenpachi, whose been stabbed in vital organs which if Naruto or Sasuke was stabbed their they'd die, also Kenpachi has greater strength then Sasuke. But I'll give this to Sasuke but it's still to early for both considering both have yet to show 100% of their true power if you get what I'm instigating in my argument.
Not only speed, go back and read the previous points. He loses due to a combination of Sasuke's speed, intelligence, hax and being a far more versatile fighter.
Also, see above, everything shown so far would indicate that Kenpachi is at his limit. Bankai? There's absolutely no proof he's awakened one, that's pure speculation, and even if he had, in his current state he can barely move, nevermind use a bankai. Sorry Kenpachi fans, was breaking through an enormous meteor and beating the strongest sternritter not good enough for you? Because that's as far as he's come at the moment, you'll have to wait a little longer if you want him to be EoS Juha Bach level or something.
Sasuke is not the one lying half-dead on the ground, barely able to move: he may have more to show. Kenpachi, apparently, does not.
I agree with you that Kenpachi has much greater endurance and strength than Sasuke, but against the things I mentioned earlier, it won't save him from losing. It will take a while, but Kenny's going down on this one.