The reason I list the "modern era" is because games played in the modern era's highlights are easier to find for the innings that are going to be listed in this thread.
Anyway, you want my take on the greatest innings under pressure?
Kamran Akmal. 109 v arch-rivals, India.
The score when Kamran Akmal walks in? 39/6, after Irfan Pathan destroyed Pakistan's top order, taking a hat-trick in what I believe was the first over.
The pitch? Very green. Nearly impossible to bat on.
But not for Kamran Akmal, he was on a mission. A mission to take Pakistan over their lowest test score (54) and then over the 100 mark.
One of the greatest knocks ever, under pressure. The series drawn 0-0, going into the final test. Green pitch. His team in big trouble, at 39/6.
He may have taken Pakistan to only 230 odd, but when Pakistan were looking to be bowled out under 70 odd, it was really a masterclass.
Because of Kamran Akmal, Pakistan recorded their highest test win vs India, and took the series 1-0. Of course, India responded with I believe 221 (?), and Pakistan made a huge 599 on a greenish pitch leaving India with no hope. However, I think on that day where Pakistan made 599, inspiration was given to them by Kamran Akmal, and the way he took his team out of that situation described and gave them the match.
Any other games / innings like this come to mind? One other game that actually does come to mind, is the Pakistan in India game in 2005, in Mohali, as well as one on this recent tour of India (by Pakistan) in 2007 by again, Akmal.
Any other innings like the one described above? These type of innings are very rare in my opinion. Another one like it, is VVS Laxman's 281 in Kolkata. Another innings from nowhere. Another innings that came when his team were down creek with no paddle to go up