Johnson started 18th on the 27-car grid for Sunday's race at the Texas Motor Speedway, a venue where he scored seven wins during his NASCAR career.
The Chip Ganassi Racing driver made good progress on track, making outside passes and rose through the field to run a legitimate fifth, before fuel worries due to faulty telemetry persuaded he and race engineer Eric Cowdin to ease the #48 car’s pace in the final couple of laps.
However, Johnson ceded only one place, to teammate Scott Dixon.
Asked if it was now valid to consider him a potential Indy 500 winner, Johnson replied: “I feel like that's an aggressive statement, for sure. But why not? Why can't we?
“The 500 is a special race. We've seen favourites win. We've seen the race won by strategy, first-time winners, a variety of different things that have taken place.
"Helio [Castroneves] is like ages older than me, [four months] and he won last year! Really, anything's possible.
“If I had a poor running today or didn't feel the car, get a sense of the car, I would think the hill to climb during the month of May would be much steeper. Learning what I did today, I'm going to start at such a better spot.
“If the race was 50 laps longer, I think I would have finished further forward. If I started 10th, the way the track played out, my result would have been better than a sixth.
“Why not? Let's dream big.”
Johnson said part of his confidence ahead of the 500 came from knowing the quality of the cars from Chip Ganassi Racing.
“I think today just showed what the #48 car is capable of,” he said. “We all know what the Chip Ganassi cars are capable of.
"I just haven't been fast enough on the street and road courses to put the car in that window and get results. To be here on a track I know, an environment that I know, I was able to provide and do that for the team.
“I feel very excited about it, very encouraged about the remaining oval races that are on the books. I know I'm going to have a great car. We'll see how it goes.”
Although Johnson completed his rookie oval test at Texas Motor Speedway last August, Ganassi did not participate in last week’s test there alongside Team Penske and Ed Carpenter Racing, after its scheduled date was shifted by three days due to bad weather.
Thus Johnson had not felt the tow effect nor the loss of downforce in turns when following other cars until yesterday’s practice sessions, so found this weekend at Texas invaluable.
“To be able to get enough laps in the race, to feel the tires from start to finish, green flag stops, being in dirty air – just how uncomfortable and treacherous that is.
"All of those little mistakes and little moments gave me a sense of the car and helped me feel really how to drive this car, how to create speed.
“Second half of the race I started working my way forward in that final stint, had a very competitive car.
"I wished that I had maybe started the race a little further forward. I think I could have finished a little further forward.”
“Not only did I grow and improve, but through my growth I've been able to give better feedback to the team. Eric made some amazing adjustments to the car, really put it into its window for that last stint. It really showed.”
