On lap 193 of 200, while Hornish was leading by more than 20 seconds, fourth placed Robbie Buhl's engine expired, bringing out the yellow and packing up the field.
The green came back out on Lap 197, but Airton Dare crashed immediately in turn 2 on the restart.
Gil de Ferran and Helio Castroneves were second and third respectively, for Team Penske in their first race of their first full season in the IRL.
The race end was one of the most controversial in history as Paul Tracy passed Hélio Castroneves just as the yellow was coming out for a crash.
Race officials ruled that the pass occurred after the yellow and declared Castroneves the winner.
Top ten results This race was held on June 16 at Pikes Peak International Raceway.
Sarah Fisher won the pole, the first by a female driver in a major open wheel series.
Top ten results Gil de Ferran was injured during a crash in this race and would miss the season finale at Texas.
Top ten results Max Papis filled in for the injured Gil de Ferran at Penske; however, he finished 21st due to a blown engine.