Importance of Warmup and Stretching

Mostly i'd do a 5 min stretching before a run, tie my shoe lases properly and start running.
Yestready was the day when i realised what mistake was i doing. I could do only 2.5 Kms at a 4.5 min pace. And at the end my legs feelt like mud! SEERIUOSLY.
I have made it a point to do good warmup and stretching before starting to run. And the result is really really satisfying. I think stretching releases the tension in the muscles and warmup gives a signal to the body that there is going to be more work load.
Now i do a routine of streches for around 15 min before and after the run. Warmup is usually a slow jog of 1 Km, which i do only on the days when i inend to run fast.
And that has helped me a lot, i must say. An advice to everybody.