Sun Yang's only opponent in the 1,500m freestyle final is his own world record.

Spearheading the 1,500m heats in 14 min 34.25 sec - almost three seconds ahead of runner-up Oussama Mellouli of Tunisia - Sun's main competition will be himself in his signature race on Saturday.

The 20-year-old smashed Australian distance swimmer Grant Hackett's decade-long world record at the Shanghai Worlds last year, clocking 14:34.14. Given his impressive performances en route to claiming his first Olympic gold in the men's 400m and the silver in 200m, Sun has almost secured his second gold in 1,500m at his Olympic debut in London.