Jake Arrieta wasn’t perfect Friday afternoon, but he was characteristically stingy when it mattered most. Arrieta worked his way out of two key jams and struck out 11 over six scoreless innings as the Cubs beat the Pirates, 6-0, at Wrigley Field. The victory was Arrieta’s 11th of the season — tying him with crosstown ace Chris Sale for the Major League lead — as he improved to 9-1 in his career vs. Pittsburgh.