Mini-broke is more common than mini-breaked among tennis fans, but Neal at Literal-Minded points out that fast-breaked is far more common than fast-broke as basketball jargon. In the baseball world, homerunned exists while Neal has not found any uses of homeran, and Pinker's original example of flied out still dominates flew out. Pinker's hockey example, high-sticked instead of high-stuck, still holds as well. So why is it that only the tennis term stays irregular?
I think that the important thing about mini-break is that it's a variation on another tennis term, break, that is used as both a noun and a verb. The meaning is so similar that slight adjustments of the examples that I found could turn them into sensible tennis statements about breaking serve during the set. For instance:
The set was pretty weird, since Guga led easily from the start, and he served at 5-3 and lost his serve... Then he broke Etlis again, finishing the game with a return winner with a backhand crosscourt.Since much of the tennis meaning of break is transferred over to mini-break, it feels appropriate for people to use the morphology of break as well. There is no analogous use of the verb break in basketball, run or fly in baseball, or stick in hockey, so people start afresh with the complex nouns and backform them into regular verbs.