Seize upon
Definition 1 of 2
Pro Tip 1/3Act Quickly
Emphasizes the speed and eagerness in taking action or deciding. 
He seized upon the last ticket to the concert.
Pro Tip 2/3Positive Aggressiveness
Shows a strong and positive determination to take an opportunity. 
She seized upon the chance to study abroad.
Pro Tip 3/3Opportunistic Nuance
Can suggest taking advantage of situations in a clever or resourceful way. 
The team seized upon their rival's weak defense.