Singapore won bronze after defeating Malaysia 2-1.
Hariss bundled home his first goal with 13 minutes gone, after the Malaysian goalkeeper fluffed his lines at a corner.
The 23-year-old then struck his second goal moments later, following great work down the flanks by Sahil Suhaimi.
Malaysia stepped up after the break and pulled one back after a defensive blunder by Afiq Yunos.
The Tigers could even have levelled at the death, but Izwan Mahbud was alert to the danger.
Singapore held off further attacks to clinch bronze, and give Malaysia their first normal time defeat in 15 SEA Games outings.
Head coach for Singapore U-23s Aide Iskandar said the achievement means little consolation for missing out on the gold, but plans are in place to achieve gold in 2015.
He said: "I believe that with good preparation, we can look forward to a good tournament.
"I think from now on, with this bronze medal, I believe that we should be working towards getting our first gold, because that is the only medal that we have not achieved at this point in time."
