He won against Dormammu. Dormammu himself is the only one that was able to perceive Strange's losses there, so there's really no reason to count them as losses from a broader standpoint (especially where the sheer volume of losses is how Strange ultimately won). By extension, even of Dormammu was the one to actually do Kaecilius in, that was a direct consequence of Strange's actions, so there's no reason not to call that a win for Strange.
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