Pirates catcher Russell Martin knocked a three-run homer in the eighth inning off Jonathan Broxton to stun the Brewers, 4-2, in front of 37,974 revelers Friday night at PNC Park. With their fifth straight win, the Bucs reduced their magic number for clinching a postseason berth as at least the National League’s No. 2 Wild Card to 5. Their lead over Milwaukee grew to 4 1/2 games.