he played first so after his attack you healed and attacked and the round was finished. so his healing was at the beginning of the round and fatigue effect is at the end of the round. because of that you were starting the round with more health.
if you were the first to attack you would lose every time.
But I'm never the first to attack in this match.
i am not sure how game determents who attacks first when speed is the same, if it is that higher lvl goes first then yes lvl 10 will always lose in this situation.
Want more proof? https://splinterlands.com/?p=battle&id=ab6af58e0d3621304365bdae1607ea5bac8b3447