"I was a miler in college," said Bor, 24. "When we got to that final mile, I thought to myself, 'This is my territory.' "
Bor found another gear in the stretch run on a reworked downtown course, winning a closely contested race in 30:20.
Defending Gum Tree champion Reuben Mwei (30:21) was second and Daniel Kirwa (30:22) - winner of last Saturday's Coca-Cola 10k in Corinth - was third. The top five runners were separated by a margin of just 16 seconds.
The fifth place finisher was Bor's brother, Julius.
Lydia Kosgei, just graduated from Eastern Kentucky, was the top female finisher in 34:49. Justyna Irena Mudy (35:04) was the runner-up.
There were 815 finishers in the race which was conducted on a new route that started on Main Street and finished at the entrance to Fairpark.
The top finishers all acknowledged that Saturday's race saw a slightly slower pace that they'd expected, at least partly due to race strategy in the face of a new, more uphill finish.
"Everyone was waiting and waiting for somebody to make a move," said Bor, who was running in Tupelo for the first time. "Nobody wanted to run out to the lead. They're all great athletes and everyone wanted to win.
"I'm pleased with the win, but not with my time."
Mwei won last year in 29:19 and praised the new race layout, even if he didn't win again.
"I like the changes, especially here at the finish," he said. "It's a much better atmosphere, with a lot more room for everyone to cool down and socialize."
The women's winner, Kosgei, praised the locals who lined up along the race route.
"This is my first time to run this race and my first time in Mississippi. It's beautiful. I love it. This race seems very runner-oriented. I especially liked the spectators along the course. When you're tired and exhausted or when you're all alone and hurting and you feel like you want to quit, it's good to hear people cheering you on. The people give me my strength to keep going."
Both Bor and Kosgei said they planned to return in 2013.
Race director Andy Hughes was tired but happy when it was all over.
"Everything went great," Hughes said. "I think that's the best we've done. The course changes, the finishing area, everything was better."