Don't open the red chest yet

I really think a key should be guaranteed.  With the current game, that's 17 successful games you'd have to play before being able to open the thing -- more, since you're likely to have a match or two that only garners one star.  That's a fairly significant amount of grinding for only a "possible" outcome.  I got a key but I can only imagine my frustration if I had not.  I know I most certainly would not be happy.