Heavy Metal War

The war gets more crowded with the sudden introduction of the Constructicons. However, rather than simply just providing raw numbers, they serve a greater purpose for Megatron. Their construction ingenuity ultimately gives Megatron every unique ability his team possesses. Of course, Optimus Prime is his primary target and in official combat. Per the terms, the loser must take his team off Earth forever. Given Megatron's current power and the Autobots being kept in the dark about it, how can Optimus possibly win this challenge?