Bronze playing in plat?

I'm bronze 4 support right now and I peaked last season at bronze 2, so I never really thought of myself as an outstanding player. But I just played a ranked game with a friend who was plat last season and we were put into a group of high Bronze/High silver summoners. It was a ranked game and I thought I was going to get crushed, but I held my own and actually came out of the game with an A. Why is it that when I play in bronze ranked games I do so poorly, but when I play games with my plat friend I seem to hold my own much better than I normally would. Why is this? And if the case is that I'm better than I think I am or I'm better than where I am placed, why am I still in bronze? Any help would be greatly appreciated!
Report as:
Offensive Spam Harassment Incorrect Board