Thatcher shot 68-65 on the weekend and it was just enough to hold off Day, who fired rounds of 62-63 over the final two days. The win was Thatcher's second of the season and third on the Nationwide Tour.
Day had been gunning for his second win of the year after he claimed the Legend Financial Group Classic three weeks earlier.
Both players have moved on to the PGA TOUR and thus will not be on hand this week.
The GOLF CHANNEL will again cover all four rounds this week.
Next week is the Wichita Open, where Brad Elder won last year.