On May 20, 2014 — Masahiro Tanaka suffers his first loss in the majors when the Cubs beat the Yankees, 6 – 1, behind Jason Hammel. Tanaka was unbeaten in 42 straight regular season starts, since August 19, 2012, including a perfect 24-0 season in Nippon Pro Baseball in 2013, although he had lost a postseason start during the streak.

Source:
Baseball Reference May 20