It’s a comeback that had looked so unlikely, even Alysa Liu’s coaches tried to talk the American teenager out of returning.

BOSTON — Alysa Liu let out a shocked smile Friday night ... Liu, 19, leapfrogged three-time defending world champion Kaori Sakamoto of Japan to win the gold with a total score of 222.97.

It’s a comeback that had looked so unlikely, even Alysa Liu’s coaches tried to talk ... dethroning three-time defending champion Kaori Sakamoto from Japan in the process.