Complex sentence: Cochrane successfully began his professional career in late 2009 amassing a 4-0 start before his first loss to future UFC veteran TJ O'Brien which saw O'Brien use his grappling to defeat Cochrane by rear naked choke early in the first round.
Split into simpler sentences: Cochrane successfully began his professional career in late 2009 amassing a 4-0 start before his first loss to future UFC fighter TJ O'Brien. Which he witnessed O'Brien use his grappling to defeat Cochrane by rear naked choke early in the first round.