You're supposed to let it play/buffer all the way till the end. Then press replay or when you're like 50-60% through the video, click on the timeline far enough back i.e < 1 min.
For example, when this video https://www.youtube.com/watch?v=2tdiKTSdE9Y finishes playing for me, and I press replay, YouTube starts rebuffering the video from scratch. In Chrome's case, the buffer is still there.