So I am doing a master's degree in mathematics in a large state school that is not very high ranked. I am planning to go for a doctorate, but not necessarily at a top school, but still an R1 school. My undergraduate degree is from Europe, and my GPA is not that great, since there was a lot of grade deflation in that school. However, it is a very good school, in top 80 on the planet.
Now, my master's GPA is quite good (3.7) right now, but the problem is: I have a B- in a core class, which is real analysis / measure theory. My previous analysis grades are pretty much all A's. I've taken other classes as well, such as algebra, number theory, topology, probability, statistics, advanced linear algebra, numerical analysis and have pretty much all A's in those. My question is: how much would this one B- affect my chances of admission?