Virender Sehwag said being struck twice on the helmet in the first hour of the Boxing Day Test gave him the confidence to put India on top on day one.
Australia tried to unsettle India with a barrage of short-pitched bowling, but Sehwag answered the call to fire a personal-best 195 in India's 329-4.
Sehwag said: "After I was hit I gained confidence because the ball only hit me on my body or my helmet.
"After that I was conscious of my
concentration going well and I played with a very solid defensive technique."
Sehwag and Akash Chopra put on 141 for the first wicket, India's first 100-plus opening stand in Australia for 18 years.
Sehwag said the two openers had stuck to a game plan to see off Australia's pace onslaught of the returning Brett Lee and Nathan Bracken in the first session.
Lee bowled with great zest on his comeback but took just one wicket
"In the morning the wicket was a little damp and the ball was
not coming on to the bat, so we decided to play defensive and not go for our shots.
"It didn't matter if it hit us on the helmet or the ribs, we would go on the defensive for the first hour and after
then we would go for a little of our shots and after lunch we would
go for the full shots."
Sehwag's fifth Test century was his most brutal yet, containing 25 boundaries and five sixes.
It bettered the previous highest first-day score at the MCG, set by Australian Clem Hill back in 1897-98. It also surpassed Sunil Gavaskar's 118 in 1977-78 as the highest Indian score at the ground.
"I played my natural game. If the ball was there to be hit, I
hit it, that's it," Sehwag said.
"I am very comfortable with my technique, so I played like I did
Sehwag was caught late in the day going for another six to bring up a maiden Test double century, but he held no regrets about his dismissal.
"I was not disappointed to get out because the ball was a full
toss and that was a loose ball, and I went for it.
"It didn't matter if I got out."
Sehwag's dismissal capped a good end to the day for Australia, who took 3-33 after India had reached 278-1.
But India, 1-0 up and chasing their first ever Test series win in Australia, still held the upper hand at the end of the first day.
Sehwag said the first hour of the second day would be important to India's chances.
"The first hour is important for us, if VVS Laxman and
Sourav Ganguly play well enough, maybe we are on the top for the second innings."