It was also the two-time F1 world champion’s first experience of both an Indycar and driving on an oval course.

"It was fun," Alonso said. "At this moment, everything looks good. Now it's time to start the real thing."

The Spaniard took just 51 laps in around an hour of running to complete the three required phases of rookie orientation.

By day's end, he had completed 110 laps, with a highest average lap speed of just under 360km/h.

"I think it's a good way to start, to build speed," he said. "It was difficult at (the) beginning to reach the minimum speed. The next stages felt good, not because of the speed but because of the laps. You're able to fine-tune the lines; upshift, downshift, which gears to use in the corner.

"The simulator is quite realistic. You have the first impression of how it's going to be. But the real car is a unique feeling. When you have to go flat out in the corner, it's not the same in the simulator as in the real car."

"The team has been amazingly helpful," Alonso said. "Running alone is quite OK. We'll see in the next weeks. So far a good experience. Now is the real deal."

Andretti Autosport chief Michael Andretti, himself a former Indy champion and a past F1 driver with McLaren, was impressed with Alonso's first run at Indy.

"He gets it," Andretti said. "He's one of the best in the world and you can see why. He had a little bit of understeer in that run and he adjusted his line because of the understeer. He's the real deal. I think he's going to be really strong this month."

Marco Andretti, who shook down the car before Alonso underwent the rookie test, said the cool track conditions combined with Alonso being the only driver on track provided an ideal setting for the initiation

"With this level of downforce, this is like race downforce, when there's no traffic and you're by yourself, it's just stuck," Marco Andretti said. "The front and rear are stuck right now, which is what you want for the first run."

"He'll have to learn by fire from a lot of it," Marco said. "But he's asking the right questions.

"He'll be fine. He's a race car driver. He'll leave today pretty confident."

Practice for the Indy 500 begins May 15 with qualifying on May 20-21. The day before practice starts at Indy, Alonso will be at Barcelona competing in the Spanish Formula 1 Grand Prix with McLaren.