"I like playing links golf. I knew coming into this run that if I get my head in the game I have an advantage," said Harrington, participating in only his second European Tour event of the season following a broken wrist.
"Today, I did a lot of good things, holed a few putts here and there and got a few breaks. I didn't expect 63 out of it. It would definitely be up there with one of the simplest, easiest, most pleasant days ever on the links.
"I know I don't have to play as well as that for the next three days. It would be nice if I did but we'll go out there and try and do more of the same. If nothing good happens for the next three days, so be it. I know I'm on the right track."
Harrington, the 2007 champion, fired three straight birdies starting from the eighth hole but had a setback at the 11th where he missed the green for his only bogey of the day.
However, the three-times major winner recovered to add further gains on the next two holes and finished with another birdie on the final one, much to the delight of the crowd.
(Reporting by Shrivathsa Sridhar in Bengaluru; editing by Clare Fallon)
