Sri Lanka's Mahela Jayawardene and Thilan Samaraweera set a Test cricket record for the fourth wicket with a 437-run stand against Pakistan in Karachi.
They beat the 411 runs compiled by England's Peter May and Colin Cowdrey against the West Indies at Birmingham in 1957.
Jayawardene scored 240 and Samaraweera made 231 on the second day of the first Test at Karachi's National Stadium as Sri Lanka declared their first innings at 644 for 7... Pakistan are 44 for 1 in reply.
Pakistan are playing their first Test match in 14 months after security problems prompted foreign teams to cancel tours of the country.
They have also been hit by an injury to strike bowler Shoaib Akhtar, as well as international bans against 17 first-class players for taking part in the rebel Indian Cricket League (ICL).