Day overcame a double-digit deficit and outscored Greensboro (NC) Dudley 27-10 in the final quarter to win 68-63.
Thomas scored 11 points as four Day players scored in double figures.
Cincinnati signee Kenny Belton led Dudley. The burly power forward tallied a game-high 31 points.
Day improved to 12-1 with the victory, its second straight championship win over Dudley in the Little 4 Invitational. The two teams last met last year in the Little 4 Invitational as Dudley featured Belton and UNC signee William Graves. Day left with the upset victory, defeating Dudley 70-54.
On the season Thomas is now averaging 19.3 points and nine rebounds. The 6-foot-5 wing was NC State's first commitment in the 2007 class.