Isolation move debate

[MrGo]

Hi - My friend and I were debating about this hand after it happened. Wanted to share it with you and see your thoughts.

24 player live tourny. About 1 hour in I am chip lead at the table. I have about 7200 in chips, blinds are 150/300.

UTG raises to 900. He has about 1600 behind him. A very weak/loose player calls from EP. He has about 6000 in chips. It's folded to me in MP. I look down and see AQs.

My thinking is this - I am 100% sure that I am ahead of the weak/loose player. He has limped in many times and is just a bad player all around. If I raise, I can isolate UTG and probably race. I didn't see why a call here would be more correct, my friend argues. I disagree with calling simply because I know I am ahead of EP. I didn't feel like UTG had AK. I had a feeling if I was going to play this hand with a raise, I would probably be in a race situation with UTG. UTG only has 1600 left so he's pretty much committed to the hand anyway.

So I raised all-in, UTG calls and EP folds. UTG turns over 99 and wins the hand as I don't improve. But I feel I made the correct play PF.

Thoughts?