LV= County Champions Durham faced a battle to avoid a season-ending defeat after Sussex took control on day two at the BrightonandHoveJobs.com County Ground.
Just 36.2 overs were possible because of bad light before play was called off at 5pm with Durham two for nought in their second innings and 162 in arrears.
Sussex had earlier reached 328 to earn a healthy lead, the hosts’ lower order staging a superb recovery from 90 for five.
Luke Wright fell 13 short of a hundred but Ben Brown and Ashar Zaidi added handy contributions of 64 and 45 respectively.
Wright resumed on 74 and showed his intent in the first over of the day when he took two boundaries off the country's leading wicket-taker Graham Onions.
He had a let off on 83 when a mis-timed off-drive just eluded extra-cover, but there was little Wright could do with the delivery that knocked back his middle and leg stump as Chris Rushworth got one to nip back and keep low. Wright’s runs came off 78 balls with 16 fours and a six.
At that stage Sussex’s lead was a modest 39 but Brown and Zaidi batted impressively in a stand of 83 for the seventh wicket.
Zaidi is playing only his second first-class match in four years and hoping to earn a permanent contract. Originally from Pakistan, he moved to England to play club cricket for Accrington in the Lancashire League and got his opportunity a fortnight ago after a successful trial in Sussex's 2nd XI.
He began today by hooking his first ball from Rushworth for six and attacked at every opportunity, hitting six fours before being caught at slip off Ben Stokes.
Brown, who had come to the crease with Sussex in trouble, reached his fifth half-century of the season and had helped his team into a strong position by the time he drove Scott Borthwick to point.
Chris Jordan was well held at slip by Paul Collingwood when he propped forward to Borthwick. Onions, who had been unusually expensive by his high standards, then picked up his third wicket after switching ends when Steve Magoffin edged to second slip.
There was a stoppage when thick mist rolled over the ground two balls into Durham's second innings. The umpires made several inspections during the afternoon but with no breeze to shift the mist the light never improved sufficiently for there to be a restart.