Pro golfer Jarrod Lyle already KO'd cancer twice ... and he's ready to do it again after a third diagnosis.

“Just another bump in my road. I will fight like no other,” he told PGATour.com.

Lyle, 35, shared the news from a Melbourne hospital on Wednesday ... where a series of tests revealed another relapse.

The Aussie's in an uphill battle ... but he has a history of sensational comebacks. 

He was first diagnosed with acute myeloid leukemia at age 17, but came back 2 years later ... eventually winning two PGA tourneys. Lyle suffered a relapse in 2012, and again fought his way back to the Tour.

Rootin' for you, J.L.