In the tiebreak, Williams was struggling until nerves got the better of Li as she made a series of unforced errors and the top seed took advantage to close it out with a second-service ace after 58 minutes.
It left him needing to serve out the set and Djokovic made what would be his final push as he attempted to recover the break, but Nadal held his nerve like a champion at 5-4, 30-30, with an ace and a service winner.
That one point never arrived as Nadal played his most brilliant tennis of the evening: forehand winner, service winner, backhand winner, ace and a strong serve to finish off the game.