Luke Wright and Ben Brown shared an unbroken 326-run stand as Sussex recovered from early trouble to close day one on 441-5 against defending county champions Durham at Hove.
Sussex had lost all of their top five at 115-5 by early afternoon as Durham's seamers did early damage after skipper Paul Collingwood chose to bowl first, including two wickets for Chris Rushworth (2-87).
But they did not strike again during the final 66 overs of the day, Wright and Brown both hitting centuries during a county record sixth-wicket partnership.
Brown, playing because Sussex's first-choice wicketkeeper Matt Prior is still sidelined by an Achilles injury, was given a reprieve by his opposite number Phil Mustard shortly before he reached 50 in an otherwise blemish-free stand.
Wright's 183 not out contained 27 fours and Brown was unbeaten on 152, including 20 fours, as both players reached their first hundreds of the season, while Collingwood used eight different bowlers in an unsuccessful effort to break the partnership.
Dexter in for the kill
Middlesex's Neil Dexter claimed career-best figures of 6-63 as Lancashire battled their way to 266 all out after being sent in at Lord's.
Jos Buttler and Tom Smith both made 59 and all of Lancashire's top nine made it into double figures.
But the Middlesex attack struck regular blows, with all-rounder Dexter sending down 10 maidens among his 26 overs to overshadow the efforts of front-line seam trio Steven Finn (2-60), Toby Roland-Jones (1-58) and Tim Murtagh (1-75).
Joe Root, Kane Williamson and Tim Bresnan scored half-centuries to lift Yorkshire to 310-8 after they had been asked to bat by Division One leaders Warwickshire at Headingley.
England batsman Root, opening the innings in place of Alex Lees, initially led the way with 11 fours in his 69 but Yorkshire slipped to 181-6 due to the efforts of Warwickshire seamers Chris Woakes (3-43), Keith Barker (3-69) and Chris Wright (2-88).
No 3 Williamson stood firm as wickets tumbled at the other end before coming on strong in the evening session alongside Bresnan, the seventh-wicket pair adding 113 in 36.3 overs.
Both fell late on with the score on 294, Williamson going lbw to Barker for 75 and Bresnan bowled by Woakes for 61.
The opening day between Nottinghamshire and Northamptonshire was lost to the weather, persistent rain preventing any chance of a start being made at Trent Bridge.