Alonso picked up the Rookie of the Year award, beating out third-place finisher and Brit Ed Jones.
The Spaniard, who was running seventh and had led 27 laps of the race when his Honda engine failed, picked up the award in Indianapolis at the traditional post-race gala dinner.
And Alonso then surprised fans with a charming speech, shrugging off the withdrawn and disgruntled figure he has cut in the F1 paddock since rejoining McLaren in 2015.
"[Fernando Alonso] has done absolutely everything to perfection with the Indy 500 – before, during and after the race. Kudos," said Twitter user 'SumSayImTheStig'.
Scott Dixon's horror crash with Jay Howard in the 101st Indy 500 Sun, May 28, 2017
Scott Dixon and Jay Howard were involved in a huge crash during the 101st Indianapolis 500
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Scott Dixon collides with Jay Howard in a spectacular crash at the Indy 500
Another, 'robwattsF1' said: "This [speech] is great. Regardless of the result, Fernando Alonso deserves respect for his efforts this month."
Fernando Alonso's Indy 500 speech in full
"I thought I should write some notes as this is probably one or two in a life time speech as I wanted to get it right!" Alonso said.
"It has been an incredible, intense few weeks since we decided we will take part in the Indy 500 and I have enjoyed every second of it.
Fernando Alonso made a classy speech to close out his Indy 500 involvement for 2017
"Maybe not that much when my car stopped – at least it was clear on which side I had to park the car as my steering has been turning left for the last three weeks, so it was clear at least on that way.
"I have always believed that a complete driver should prove himself in a different series of motor sport and this is one of the reasons why I came here.
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"We entered this race also with the aim of linking two different worlds of motor sport and I believe we have achieved this.
"In spite of Tony Kanaan's several warnings, I'm glad I can say I have made it nearly unscratched through the whole month of May, it's the first time I do so many activities off track, so many photos, so many autographs, we even flew to another city in the middle of the event, for you guys this is normal, but trust me it's not normal!
Fernando Alonso has clearly enjoyed his time at Indy 500 in a competitive car
"Then, you want to focus and concentrate on the race so you come to the grid and hardly can find your car, so finally you jump in the car and you think that you are finally alone and concentrated but you have two spotters who tell you how to drive inside, outside.
"It has been a privilege and an honour to take part in this iconic race and I want to thank everyone who has made this possible.
"Thanks to McLaren-Honda and Andretti who gave me this great chance, Michael thanks for welcoming me so warmly, everyone at Andretti Autosport has made me feel at home and I can say I have found a new family here, what a team.
"Thanks to Zak Brown and everyone at McLaren and Honda for the great effort and energy you have put into this project. Thanks to all my team-mates, Ryan, Marco, Alex, Jack and Taku, who have looked after me and given me all sorts of tips.
"Taku of course, congratulations for winning this one but the next time, I want your engine!
"And you are my favourite Japanese driver in IndyCar!
"Thank you all the drivers, I'm so glad I have found some great people and friends on this side of the Atlantic.
"You guys are so talented, I watched so many, many videos on Youtube before coming here and racing these two weeks together I learned so much from each one of you, that has made me a better driver today, not only in oval racing, so thank you guys.
"Thanks to Gil de Ferran, 'obrigado' my friend, my brilliant coach, and Johnny Rutherford, my girlfriend Linda, my physio Fabrizio and to my best friend Alberto who have shared with me this exciting journey.
"Silvia, my press officer, who has worked with me the last three years at McLaren, I mean for her this was the last three weeks very intense, but she enjoyed it so much, I think for a press officer this event is like Disneyland for any kid, so I'm happy she enjoyed it.
"It has been an amazing experience that I will take with my forever, I cannot wait to have my papaya orange car in my museum in Spain, finally I would like to wish a speedy recovery to Sebastien Bourdais, we have missed you on track man, get well soon also to Scott, I saw you with some things on your hands, was an incredible flight.
"Thanks everyone, thanks Indianapolis, thanks IndyCar."