Parker recorded a steady 2-under-par 70 in the final round to win the Georgia Junior Championship by two shots at Augusta Country Club.
"I thought he'd win before the tournament started," Harbin said. "He doesn't shoot over par on this course. And that's what you've got to do to get it done."
Parker, who opened with rounds of 69-70 and finished at 7-under-par 209, began the day two behind 36-hole leader Lee Knox, of Augusta.
But Knox turned in his worst round of the event with 74 to finish second at 211.
"I know what it takes to win, I just didn't execute," Knox said. "I just didn't get it done."
Valdosta's Trey McQuaig (70) and Bogart's Blake Soni (72) tied for third at 215. Harbin (74) and Clark Palmer (73), both of Augusta, tied for fifth with Cameron Simmons, of Acworth, (76).
By finishing in the top eight, Parker, Knox, Harbin and Palmer will represent Augusta Country Club as well as the Peach State in the 33rd annual Georgia-South Carolina Junior Challenge Match at Hawks Ridge Golf Club in Ball Ground, July 18-19.
Harbin said making the team was a pre-tournament goal. So when he dropped a 30-foot birdie putt at No. 18, he said he felt relieved.
"I thought I had to make that," said Harbin, who only needed a par. "It felt good anyway."
Parker started feeling good about his round after rolling in an 8-foot birdie putt on No. 5. He followed with another birdie, draining a 35-foot putt on No. 6. He then added another short birdie putt at the par-5 eighth.
Parker then two-putted every green on the back nine, carding par on every hole except for a bogey at the last.
"Usually, putting is not the best part of my game," Parker said. "It was just there."
Parker pulled into a tie for the lead after Knox drove into the pine trees right at No. 11 and settled for bogey. Knox then added a three-putt bogey from 30 feet at No. 13.
Down two, Knox reached the back of the green at the par-5 15th in two.
But he left his 45-foot eagle putt short and then he failed to convert his 6-foot birdie attempt.
"I hit good putts. They just didn't go in," Knox said. "I always had a putt at it but I was never close enough to get the ball in the hole."
The 17-year-old Parker finally got in the win column after posting three runner-up finishes in a pair of junior events and the Augusta Country Club championship within the past month.
"To win," the rising Westside High School senior said, "feels pretty good."
Reach Chris Gay at (706) 823-3645 or firstname.lastname@example.org.