Harris shot an eight-under 27 on the back nine at The Club at Indian Creek with six birdies, an eagle and two pars added to four birdies and five pars across his front nine in Nebraska.
The 23-year-old, who beat Alistair Docherty in the play-off after both players ended at 22 under following the regulation 72 holes, is the ninth golfer worldwide to shoot a sub-60 final round and win the tournament.
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Harris joins players including Bryson DeChambeau, who won LIV Golf Greenbrier in 2023 after ending with a 58, and Jim Furyk, who recorded a 58 in round four of the 2016 Travelers Championship.
'Shooting a 59 never crossed my mind'
Harris said afterwards: "The thought of a 59 never even crossed my mind. Honestly, like 100 per cent. I did not know I shot a 59 when I made that putt on 18.
"I knew I was playing well, but I was just trying to keep the pedal on the gas and finish strong.
"I was ready to crack my first beer once I finished the round, but then my caddie and I made a smart choice not do that because Alistair came in real hot.
"I knew it was going to come down to a play-off, so figured it was my time."
The victory moves Harris to No 29 on the Korn Ferry Tour points list, with the top 20 at the end of the campaign earning PGA Tour cards for 2027.
The PGA Tour's FedExCup Playoffs begin on Thursday with the FedEx St. Jude Championship. Watch live on Sky Sports Golf and Sky Sports Main Event from 7pm or stream with no contract through NOW.
