Harrell's two-run homer off Patrick Johnson over the left-field bullpen followed Conrad Gregor's tying double off the top of the wall. The Commodores added two runs in the eighth.
Corey Williams (2-0) worked 2.2 innings of scoreless relief for Vanderbilt starter Sonny Gray.
Johnson (13-2), who had allowed three earned runs in his previous 45 innings, was tagged for four earned runs and five total in six innings.
Vanderbilt (53-10) advanced to a Bracket 1 game Monday night against Florida. North Carolina (50-15), which left 16 men on base, plays Texas on Monday afternoon.