A similar thing happened in my last game.
I was playing Brand against a LeBlanc. I was doing pretty well, out csing her and zoning her away from my minions by W>E and spreading my flame to her.
Every time she wanted to trade I would E her then q her as she dashed to me, stunning her. I would then W and walk away, I wouldnt be unscathed but I would always force a passive burn and a back.
After buying a negatron cloak it was even easier to bully her, keeping the lane pushed and keeping her from roaming.
However one time I brought her low and she left, their half health Elise came from top to gank me. I saw her coming a mile away and E Q stunned her as soon as she cocooned me, then LeBlanc blinked over to try to help.
I threw my ult into their midst then flashed away.
I got a double kill. I went on to carry our struggling top lane and got a victory through attrition.
The moral of the story is never gank a Brand with his ult up while he has mana and you have low health, even if you have some CC.