Josef Newgarden finished second and Will Power was third. Indianapolis 500 winner Takuma Sato took fourth and Simon Pagenaud came in fifth.
Rahal led 55 laps in Saturday's race and another 41 laps on Sunday. He won the first one by 6.14 seconds and the second by 1.1772 seconds.
Rahal had a seven-second lead when a late caution waved Sunday, and he had to sit through a 20-minute red flag as officials cleaned oil off the track from two unrelated engine failures.
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Rahal became the first driver to win two races this season, and of the five doubleheader events (10 races) on the temporary street circuit, he is only the third driver to win for a second time. The others are Sebastien Bourdais and Power.
(Editing by Gene Cherry)
