Same route as yesterday, only in reverse

Strange how things seem when you see them from another perspective. I decided earlier today that I would run my usual 10k route but from back to front. It seemed as if it might be a little easier taking a couple of hills out of play or just shortening them up some. I really didn't feel like running fast but by the time 2km came around I was well on my way. I kept as quick a pace as I could handle as the km ticked by. The route familiar as it is was technically different as the rolling hills roll more in this direction and my course markers were a little different as well. At 9km, I opened everything up that I had left and ran full tilt, as hard as I could to the end. Hard, that is it. I was really moving. At the end, my pace per km had dropped by 4 seconds so I knew I had ripped. When I got home, that last km was clocked at 4:10. Holy shit, that is really fast. That is a sub 21 minute 5k. Or better yet, if I could hold that pace, a sub 3 hour marathon. Dare to dream right?
Anyway, it was awesome and fast but my legs feel like freshly setting concrete. Thank goodness for the day off tomorrow. 48:03 ~ 10km, 4:48 per km.