Choi, the first South Korean to win a PGA Tour title, collected his second win of the year to go along with the Compaq Classic in May.
Four birdies and a lone bogey propelled Choi to the largest margin of victory on the tour this year. Ranked 31st on the money list coming into Tampa Bay, Choi's first place check of $468,000 assures him a spot in the upcoming Tour Championship.
'When I first started out the day I did feel some pressure and uneasiness to be honest, but as the holes went by I felt much more comfortable,' Choi said through an interpreter. 'I just said to myself, 'I'll just take it hole by hole.''
Day, who a shot a 2-under-par 69, was never able to put pressure on Choi, but his 10-under four-day total was good enough for sole possession of second place.
Mark Brooks posted one of the day's low rounds with a 4-under 68 to finish alone in third place. It was only his second top-10 of the year, but matched his third place at The International in August.
John Morse and Rod Pampling tied for fourth at minus-8. Morse used a four-hole birdie streak to start his day to climb into the battle for second.
Pampling, who was in second after the first and second rounds, shot 73-70 on the weekend and left Choi alone at the top.
Rookie of the Year candidate Pat Perez played in the final group with Choi, but stumbled in with a 3-over-par 74 that left him in a tie for seventh at 5-under.
Peter Jacobson and Matt Kuchar were a stroke back, each closing with 1-under 70s.
Ty Tryon made his first cut as a rookie but a final round 75 dropped him from 20th to a tie for 41st. After a bogeyless Friday that included six birdies, he could only managed four more over the weekend.
Choi came into this week 31st on the money list, one spot away from qualifying for the lucrative WGC-American Express Championship, which Woods won in Ireland this week.
'I really wasn't disappointed about(not) getting into the American Express Championship,' said Choi. 'I just accepted it and the only other alternative was to come back to the States to play this tournament.'
Final scores from the Tampa Bay Classic