The context of the following conversation is Alex is a professional athlete.  He bet some strangers that he could win a race and won.:
Alex says I bet I can beat you guys in a race..
The friend responds I mean, I know you're a pro, but these are some fast guys..
Alex responds Well, I bet you, I can beat them..
The friend responds OK, you're on..
Alex responds  I won!.
The friend responds Man, you really are fast..