Pole starter Shawn Strand led the first lap before Mark Dahl drove by. Thornton had started ninth, was in the runner-up position by lap five and then used the high line to take charge up front on lap 12.
He used multiple lines in building his lead and had caught up with the back of the field before the only caution of the contest came for the mandatory pit stop on the front straight after midway.
Shryock had moved into second just before the yellow. He was side-by-side with Thornton after the race resumed and the six circuits were scored.
The second half of the Legendary was worth the price of admission alone as the front two battled high and low, Thornton finally using his momentum off the top side to edge Shryock at the finish by the narrowest of margins.
Heat winners were Shryock, Grimes, Taylor, Friestad, Stone, Elliott, Strand, Thornton, Dahl and Ulmer.