"To see a team here in Jackson that wasn't very good last year, win a championship this year, it's a very special night for a lot of people," Generals manager Daren Brown said.
The championship caps a spectacular season for O'Neill, the Mariners' No. 2 prospect.
O'Neill led Jackson to an 84-55 record, best in the Southern League, with a .293/.374/.508 slash line in 130 games. The 21-year-old also showed why he's regarded as the No. 62 overall prospect by adding 24 homers and 102 RBIs.
"He's somebody that we counted on every night, he got a lot of big hits for us," Brown said. "You look at him and you see the power numbers, you think power. But, he put up good at-bats all season and to cap it off with a championship and MVP, it was a special year for him."
It was more of the same in the playoffs, as O'Neill hit .448 with three homers and eight RBIs in seven contests, including a 3-for-6 night in the clinching game.
The Generals jumped out to an early lead and never looked back, leading from the top of the first through the bottom of the ninth.
Braves' No. 28 prospect Patrick Weigel had a tough time finding the strike zone -- walking five in two-thirds of an inning -- and the Generals patiently built an early lead.
Jackson registered just one hit in the first inning but drew six walks, sending 10 men to the plate and scoring four runs.
Mississippi cut the lead to one in the third, but O'Neill and company tacked on one in the fourth, three in the fifth and three more in the seventh to break the game open.
In addition to O'Neill, Benji Gonzalez (two RBIs), Tim Lopes, Dario Pizzano (two RBIs) and Tyler Marlette (three RBIs) also had multi-hit efforts.
Mariners' No. 18 prospect Paul Blackburn wasn't at his best, but he did enough to hold off Mississippi and let his offense take over. The right-hander surrendered 11 hits but limited the damage to three runs in six innings.