There is no chance in hell Maul would beat Anakin (Vader). Obi-Wan managed to cut Mauls saber in half (which was a potential killing blow) and keep him on the run when he was a padawan. Anakin is WAYYYYYYYY above TPM Obi-Wan....lol Anakin is just below Yoda and Mace in the entire Jedi order in terms of saber combat (and arguably Obi-Wan but its not as cut and dry as with Yoda and Mace)
Vader would tool Maul, then crap on his mangled corpse.
Even considering the Infinity, Vader (according to the Prophets) was emotionally conflicted inside. It's possible Maul was aided by Dark Side prophets.
Anyways, Vader does cut his saber in half. Luckily for Maul, he cuts it at the exact spot where it'll form dual sabers >_>
And let's not forget, Vader does win. He took a hit through the chest and just walked away.