Kevin Pietersen rated his unbeaten 202 at Lord's as the toughest innings of his career.
Pietersen made his fifth century at the Home of Cricket, in his longest innings for England, to put him just one behind Michael Vaughan and two behind Graham Gooch for the most tons at Lord's.
He overcame some extremely seam-friendly conditions early in his knock, taking 134 balls to reach his first 50, and was well past his hundred before finding his dominant best.
The last fifty runs of his mammoth total was racked up in just 25 balls though as he helped England towards an imposing declaration total of 474-8.
The nature of his 18th Test ton, and first in England since 2008, made the day particularly memorable for Pietersen.
"It's something to be proud of definitely," said the 31-year-old number four.
"There are some fairly complimentary things being said to me in the dressing room. With the conditions I batted in yesterday, the wicket and having to face Mahendra Singh Dhonni for half an hour as well - I think it's up there with the hundreds I've scored.
"I've never had to work that hard. They bowled real well in the swinging conditions. It was real hard graft."
Batting conditions - so treacherous on day one - appeared to get easier on an even paced Lord's track, with India's bowlers tiring in the absence of Zaheer Khan and even relying on eight overs from 'keeper Dhoni.
But Pietersen insists there is enough still in the pitch for the England attack to trouble the India batsmen, who are in unfamiliar conditions.
"The wicket that we're playing on at the moment is still offering a lot for the seamers. It's swinging, and if it swings, it's alien to the India batters." he added.
"To be put in to bat and be 274 runs up; we're in a pretty good position.
"Every single next day is an important day so tomorrow is crucial, as is Sunday and, if we get to Monday."
Pietersen's Indian Premier League team-mate Praveen Kumar starred for India, taking 5-106 in a skillful display.
The pair exchanged words during the evening session but Pietersen played down the exchange, and was full of praise for the 24-year-old seamer.
"PK [Kumar)] is a very good friend of mine, I captained him for a year [in the IPL] and he never listened to me!" added Pietersen, who was celebrating his second double century at Lord's.
"I'm joking. PK's a really good, skilled bowler and if there's one bowler in the India team who I'm happy to see get the five wickets it's PK because I spent two seasons in the IPL with him and he's a fantastic guy."
Kumar, playing in only his fourth Test match, described his day at Lord's as a "dream".
In the absence of the injured Zahher Khan he assumed the mantle of leading the India attack, a role he relished.
Kumar said: "It was not a question of pressure to fill in for Zaheer, it was just a question of motivating myself.
"I'm used to bowling 30-35 overs in domestic cricket as well. I liked it."