It is a common misconception that only a single sperm is needed for fertilization to occur.
In fact, the first sperm to reach the egg is never the one to fertilize it.
Hundreds of sperm are required to prepare the way for the final sperm 'survivor' to fertilize the egg.
These hundreds of sperm undergo acrosomal reaction, breaking down the outer two protective layers of the egg until a path is created to allow for the 'winner' to clinch the 'prized' egg.
In order to get a few hundred sperm reaching the egg, a few million sperm need to reach the uterus.