I am going to burst your bubble: The English language disagrees with your opinion
When there is a battle between X and Y and both kill eachother, then it is a draw. There is no Winner. Loss is what happens when either X or Y dies and the otherone survives. In order to even be able to win against Deidara, you need to be able to survive his self destruction or prevent it from going off. I named the people who are capable of surviving it, there might be some old Kage's or something that I didn't name.
Regardless, Sai not only isn't able to survive that explosion, he isn't even able to defeat Deidara.