Maybe the problem is not to have an entry for /usr/bin in your PATH (usually on a working system is already there). You have to check the order in which directories are stored in PATH: when you run a command like simply
the system look for an executable in the directories specified in the PATH variable, one after one. The first encountered is the one executed.
Also, the already suggested "make uninstall" from the installation source can solve the problem (further re-installation of the RPM is useful only if the two installation had common places for libraries, configuration files and so on...).
Another solution, if you don't want to uninstall, is to remove the executable bit from the first binary executable. Suppose you have installed it in /usr/local/bin, just do
chmod -x /usr/local/bin/mplayer