Yorkshire endured another frustrating day at the office after Tim Ambrose negated a fiery opening from the reigning champions.

Ambrose came to the crease with Sussex struggling on 40 for three but defied the difficult conditions to strike an unbeaten 146.

He was ably supported by wicket-keeper Matthew Prior, who hit 83 and shared in a 191-run partnership with Ambrose for the sixth wicket to swing the balance of the game.

Yorkshire are desperate to notch their first win of the Championship season, and it showed as they sent Sussex in to bat and won the early exchanges.

Steve Kirby, last week handed three penalty points for indisciplined behaviour against Leicestershire, struck first to trap Richard Montgomerie lbw for 11.

Chris Silverwood then removed Michael Yardy (three) and Murray Goodwin (18) in quick succession.

A 30-run stand for the fourth wicket between Ambrose and Phil Cottey was then broken by Ryan Sidebottom, and when Robin Martin-Jenkins (30) fell to Kirby with the score on 121 Yorkshire were well on top.

But Prior strode to the crease and a promising start by Yorkshire was turned on its head.

Prior was more the aggressor, hitting 12 fours and two sixes from 141 balls while Ambrose contented himself with 19 boundaries in a 273-ball knock.

Craig White intervened to have Prior caught behind late in the day, but by then the damage had been done - or in the case of Yorkshire, reversed.

Yorkshire: M J Wood, C White, M J Lumb, S M Katich, A McGrath, V J Craven, R J Blakey (Capt, Wkt), G M Hamilton, C E W Silverwood, R J Sidebottom, S P Kirby.

Sussex: R R Montgomerie, M W Goodwin, M H Yardy, P A Cottey, T R Ambrose, R S C Martin-Jenkins, M J Prior (Wkt), K J Innes, M J G Davis, R J Kirtley (Capt), B V Taylor.

Umpires: M J Harris and D R Shepherd