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Anything you do with charisma and a smile will get a positive reaction 8 times out of 10.. Unless the girl has deep personal issues.. A direct approach works for me but im sure that'll work.. It's not what you say, its how you say it.
This is definitely spoken from someone with a lot of experience opening sets! 
It really is not what you say, it is how you say it. Personally, I think going "Direct" here is better because it is more alpha, shows you have more balls than trying to slide in like you really wanted directions. She knows you like her so why front?"Hi, I know this is totally random, but I saw you over here and had to come introduce myself. My name is xxxx."
Regardless of what you decide to do, have a upbeat positive attitude, good eye contact, and smile. The rest will be pretty easy. From there just understand with day game girls are busy, they are typically running errands and stuff. They may not have a lot of time to hang. Have a close bounce location like a food court or coffee shop to sit them down for a few to talk, and then go for the #.