Watch highlights of day one
Records fell at the BrightonandHoveJobs.com County Ground as Luke Wright and Ben Brown compiled an unbroken triple-century partnership for Sussex against Durham.
The pair came together with the hosts at 115 for five in the LV= County Championship Division One clash and remained there at the close having put on 326.
The stand is Sussex's highest for the sixth wicket, beating a record set in 1930, and the highest sixth-wicket alliance for anyone against Durham.
Wright, on 183, is just four runs short of equalling his highest first-class score, while Brown ended the day unbeaten on 152, 40 more than his previous best, in Sussex's 441 for five.
Thanks for all the nice tweets. Very enjoyable batting with @Ben_Brown26. Hopefully build on it. @graynicspic.twitter.com/FCHmlvYhOn
— Luke Wright (@lukewright204) May 11, 2014
Defending champions Durham, who are looking for their first victory of the season, won the toss and put Sussex in, and for a time it looked a good decision.
Chris Nash was the first man to go, edging Chris Rushworth behind for 10, and Michael Yardy then fell for just five when he was caught by Kumar Sangakkara off Graham Onions.
Wickets continued to tumble - Ed Joyce bowled by Usman Arshad for 21 before opening batsman Luke Wells gave wicketkeeper Phil Mustard a second catch.
And when Matt Machan also edged behind to depart for 22, Sussex looked in some trouble at 115 for five.
But little did they know by the close of play Wright and Brown would have guided them to 441 with no further wickets lost.
WATCH: Here's the thoughts of @lukewright204 as he spoke to @BBCSussexSport after play today at Hove #GOSBTShttp://t.co/aWZyX3W8cH
— Sussex CCC (@SussexCCC) May 11, 2014
Durham did have a chance to snare Brown but Mustard dropped his fellow wicketkeeper.
His misery was then compounded the following ball when Brown stole a single, Mustard shied at the stumps and conceded four overthrows, allowing the Sussex man to reach his 50.
With first-choice wicketkeeper Matt Prior still sidelined by an Achilles injury, Brown certainly took his chance to impress.
Sussex, who were usurped by Warwickshire at the top of the table after rain in Manchester on Wednesday, will now hope to press home their advantage tomorrow.