But famed team owner Roger Penske was convinced Montoya could find Victory Lane again, and brought him back to IndyCar last year after his NASCAR contract wasn't renewed.
Montoya rewarded Penske's faith Sunday by winning the Indianapolis 500 for a second time — 15 years after the 39-year-old Colombian's first win at the Brickyard.
Montoya passed Australian Will Power — his teammate and the reigning Verizon IndyCar Series champion — with three laps left and held on for the victory in the 99th running of the Indy 500.
As he crossed the finish line, "I was screaming I was so happy," Montoya said.
Power finished second, Charlie Kimball of Camarillo was third and pole-sitter Scott Dixon, Kimball's Chip Ganassi Racing teammate, finished fourth.
All four battled at the front of the pack in the closing laps, with Montoya and Power swapping the lead several times at the 2.5-mile Indianapolis Motor Speedway.
"That fight there at the end . . . that was awesome," Montoya said after taking Indy's traditional sip of milk in Victory Lane.
Montoya's win gave Penske a record 16th team owner's victory in the Indy 500, and his first since Helio Castroneves won in 2009.
Castroneves on Sunday finished seventh, and thus again fell short in his bid to win a record-tying fourth Indy 500.
Montoya won his first Indy 500 with Ganassi, and then drove for Ganassi during his NASCAR stint from 2007 through 2013.
He spoiled Ganassi's 57th birthday on Sunday but said his former team owner congratulated him after the race. "We're still good friends," Montoya said.
Of his current seat with Penske, Montoya said, "I'm glad I am proving them right and that they made the right choice."
The win capped his remarkable comeback during the race. He started 15th, and a rear bumper panel on his car was knocked loose by the car of Simona de Silvestro on an early lap, forcing Montoya to the pits. The setback dropped him as low as 30th in the 33-car field.
But he steadily moved back through the field and, with less than 15 laps left, was swapping the lead with Power and Dixon until Montoya grabbed it for good.
"Montoya coming from all the way in the back — I'll tell you, you give that guy the bit . . . he doesn't give up," Penske said.
At the same time, Montoya said, "We kept adjusting the car and it was a little better, a little better. We executed today beautifully."
A fourth Penske driver, Simon Pagenaud of France, led 35 laps until he faded late in the race and finished 10th.
The leaders' shootout was set up by a crash with 22 laps left in the 200-lap race that collected Sebastian Saavedra, Jack Hawksworth and rookie Stefano Coletti.
It was one of several accidents in the race, but none of the cars got airborne as they had three times in practice crashes earlier this month.
The race got off to a messy start after NASCAR star Jeff Gordon, driving the pace car, led the field to the starting line and actor Patrick Dempsey waved the green flag.
Sage Karam and Takuma Sato promptly collided and crashed in Turn 1. That knocked Karam out of the race and caused the first 12 laps to be run under a caution period.
Ed Carpenter and Oriol Servia were involved in another crash on Lap 113, with both cars too damaged to continue.
And 2013 Indy 500 winner Tony Kanaan, who was running in the top five for much of the race, lost control and crashed into the wall on Lap 152.
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