Seize the upper hand is an encounter power available to warlords at 1st level.
CharOp Evaluation: Average [Charop Warlord]
This is a solid power... if you can maintain combat advantage. The fact that most enemies will be smart enough to shift out of flank seriously impacts the effectiveness this power, unless another power is used to force the enemy to stay stationary, which is another opportunity cost that makes it less appealing.