Why are the powerball and mega millions odds the same for 2nd Place Prize?

It says on the back of both play cards the odds of matching 5 out of six and not matching the mega or powerball are 1:in 3,904,701. But Powerball has more 1 -59 and Mega has less 1 -56. So If Powerball uses 3 more balls how can the odds be the same? They cant be. The odds of matching 5 out of 6 in powerball are more like 1: 5,138,133.