The determined Brazilian came from last place to lead the most laps and win the PEAK Indy 300 at Chicagoland Speedway in a photo finish -- and it wasn't enough.
The 28-year-old Dixon, driving for Target Chip Ganassi Racing, held a seemingly insurmountable 78-point lead heading into the last three races of the season. But Castroneves put on a late-season charge that included both of his 2008 race wins and put a definite scare into the New Zealander.
"I think we set our minds on having [the championship] tied up a long time before now and I think that's what run us into a bit of trouble," Dixon said. "That was definitely the toughest two weeks I've had and, even today, Team Penske and Helio wouldn't let it go. They were pushing to make sure they got the most. You've got to take your hats off to them for doing all that they needed to do."
Castroneves won the race in the second-closest finish in the history of the IndyCar Series, winning by 0.0033 seconds, which translates to 12 1/8 inches. It was so close that Dixon was initially declared the winner and went to Victory Circle before race officials studied photos of the finish and gave the win to Castroneves.
Only former Team Penske driver Sam Hornish Jr.'s 0.0024-seconds win over Al Unser Jr. in 2002 on this same track has been closer in the 13-year history of IndyCar.
"It was the craziest Victory Circle I've been involved in, where you see your car rolled into position, you get out like you won the race and they roll it off and take your hat off you and say you haven't won," Dixon said. "That was tough to deal with but, in the back of my mind, we all knew we'd won the championship, and that was the main goal."
Dixon knew coming in he only had to finish eighth or better Sunday to win the title and, after struggling in the middle portion of the race, he left no doubt at the end about the championship. He came into the race with a 30-point lead and wound up winning the title and the $1 million bonus that goes with it by 17 points.
It was sweet redemption for Dixon, who lost both the race and the title to Dario Franchitti last year at Chicagoland Speedway when he ran out of fuel two turns from the finish.
It was far from a perfect race for Dixon, who didn't lead until 15 laps from the end and fell as far back as 11th in the middle of the 200-lap event. But he came on strong when he had to and was able to celebrate the title, hugging team owner Chip Ganassi and getting pounded on by his crew.
"The year on the whole has been amazing, an unforgettable year," he said. "I still can't believe getting married, winning the Indianapolis 500 and winning the championship, not too many people can say they've done that in one year."
The champion acknowledged he got a little worried in the middle of the race when he slipped back into the pack.
"It was tough, especially when you're racing around 10th," Dixon said. "You've got people in front of you, people behind you and they're all trying to do crazy things and it's really tough to keep yourself calm and know that you've got the car to get to the front and just wait for a green-flag run to make it happen was happen was probably the hardest part."
His pit stops were not great most of the day, including one in which a tire briefly got away from one of his crewmen, but Dixon said the last stop was perfect.
"The crew guys, they might have had one problem there, but look what they did at the end," he said. "They brought us through."
Castroneves, who earned a 3-point bonus by leading a race-high 80 laps, was excited after being told he won the race when he got out of his car.
"I knew I won it, I knew," he said. "We try everything, everything, to win. We did everything we could.
"I feel [like] he respects me and I feel the same way, with a lot of respect. That's why, toward the end of the race, you're able to ride side-by-side, inches [apart], wheel-to-wheel without worry that's he's going to play dirty or something like that.
"I was able to go on the last lap and pull alongside and said, 'OK, now we got to do what we got to do.' It was fun," the race winner added.
Dixon became the fourth straight Indy 500 winner to go on to earn the series championship, following Dan Wheldon, Hornish and Franchitti.
The champion gave the Ganassi team its sixth open-wheel title, including four in the now-defunct CART/Champ Car series. Ganassi's team of Scott Pruett and Memo Rojas also wrapped up the Rolex Grand-Am Sports Car Series championship a week ago.
Dixon added the title to the one he won in 2003, his first year in IndyCar, by racing all season with consistency. He finished with a record-tying six victories and 14 top-five finishes in 17 starts.
Things looked bright for Dixon and particularly bleak for Castroneves on Saturday when the Brazilian qualified fourth, but was penalized to the rear of the 28-car field for driving under the white out-of-bounds line at the bottom of the banked oval on each of his four laps.
But the determined Castroneves, trailing Dixon by 30 points and knowing he had to win or finish second and lead the most laps to have any shot at his first series title, gave himself a chance by charging from the green flag.
His No. 3 Team Penske Dallara sliced through traffic, moving quickly into contention. Castroneves got to 10th on Lap 20, passed Dixon for third on lap 66 and took the lead by beating teammate Ryan Briscoe out of the pits during a caution flag stop on lap 78.
Meanwhile, Dixon came into the last points race of the season knowing he was vulnerable again, thanks to the late-season charge by Castroneves, who finished the season with two victories and eight second-place finishes. Castroneves finished no worse than second in his last six starts.
Dixon started next to pole-winner Briscoe but never led until 15 laps from the end when he came out of the pits about 3 feet ahead of Castroneves after their final stops.
From that point to the end, it was a two-man race, with Castroneves chasing Dixon. He finally got alongside Dixon on Lap 199 and each got a nose ahead several times until Castroneves somehow managed to lead at the finish line.