The Irish native looked inside, then darted outside and outraced three other drivers down the front straightaway to win Friday's Freedom 100 by 0.026 seconds over Colombia's Gabby Chaves -- the closest oval finish ever on the world-famous 2.5-mile oval that has hosted races for more than a century, since 1909.
"It was unreal," said Dempsey, who drives for Belardi Auto Racing. "Fortunately, we had just enough room to squeeze by. You're not going to get better than four wide coming across the line."
It was unlike any finish IndyCar fans had ever seen at the historic venue.
Firestone Indy Lights points leader Carlos Munoz was in line to earn his third straight win in the series when Chaves and pole-sitter Sage Karam spread out to make it three-wide coming down the home stretch. Then Dempsey made his move, getting outside of Chaves and using the draft and his car's momentum to slingshot his way past the other three drivers just before crossing the yard of bricks. It was the first career win for Dempsey on IndyCar's developmental circuit.
"I thought it was going to be three-wide to the finish and all of a sudden here comes Peter and I'm thinking, oh my gosh, how can I make my car wider," said Chaves, who drives for Schmidt Peterson Motorsports along with Karam. "He got me at the end."
Most of the eyes had been focused on Munoz throughout the race.
The Colombian with Andretti Autosport had been impressive all month at Indy. He came into the race with two straight wins in the Lights series and was trying to make history in a different way at Indy -- becoming the first driver to win both Memorial Day races at Indy. He came close before settling for fourth.
The consolation prize is that he will start second in the weekend's biggest race, Sunday's Indianapolis 500. He's the first rookie to start from Indy's coveted front row since Juan Pablo Montoya, also from Colombia, did it in 2000, when he won the race.
"I'm Ok, I'm not disappointed at all, I gave everything on the track," Munoz said. "I have to think more about the championship than winning the race and that's what I did. There's a long, long way to go."
Munoz took the lead on lap 13 and led narrowly over Karam, the pole-sitter, the rest of the way until the cars spread out across the final straightaway. With about two laps to go, he even considered dropping out of the lead to pick up a draft. Instead, he stayed in the front and it cost him when Dempsey made his move.
Two drivers, Kyle O'Gara, who drives for his sister-in-law Sarah Fisher, and Jack Hawksworth, another of Sam Schmidt's drivers, were both knocked out of the race in minor crashes.
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