No excuse for any duelist to lose to Mai.

For much of the season, Mai was the lone female duelist but she's a terrible player, she relies too heavily on cheap tricks, buckles when her strategies fail and only duels players so low ranked you wonder how she got so far.
To compare against other female characters of the season.
Anzu - Doesn't know what she's doing but somehow was the only duelist to have zero losses.
Serenity - Not really a duelist.
Rebecca - Duels competently despite having a lousy win/loss record.
Vivian - I honestly forgot she was in the show but she was introduced as the Asian champion so she at least has some skill.
Ishizu - Best female in the show and should've had more duels.
The history of female duelists hasn't exactly been that strong, even later seasons have introduced argubly better duelists but their impact on the show has been very little, even Asuka and Akiza have had their roles shortened as their season went on, if you don't start your female characters strongly you don't grab that demograph and Mai set a very poor standard that is still being felt today.