Gloucestershire 417 and 81 for 6 (Seales 2-12, Robinson 2-32) lead Sussex 479 (Pujara 86, Alsop 84, Lamb 83, Simpson 79) by 19 runs
Ollie Robinson took two wickets in three balls as Sussex put themselves in a strong position to claim their first win of the season in the Vitality County Championship.
Having bowled 27 wicketless overs in the match, Robinson was finally rewarded when he pinned Cameron Bancroft and James Bracey leg before as Gloucestershire slumped to 27 for 4 in their second innings. They reached stumps on 81 for 6, leading by just 19 at Hove.
Ben Charlesworth pulled his third ball over mid-wicket for six, but Robinson quickly settled into an impressive rhythm at good pace down the slope and was rewarded in his sixth over. Bancroft played across a ball which cut back that would have hit leg stump and Bracey, offering minimum footwork, was plumb in front of a straight one.
Robinson's workload is being managed by the ECB and his 9-3-21-2 spell was his longest - and best - spell of the season so far. He bowled four more testing overs and had 2 for 32 from 13 overs at stumps - with power to add tomorrow.
Jayden Seales had taken two wickets in his first two overs after Gloucestershire had gone in again trailing by 62 on first innings having dismissed Sussex for 479.
Charlesworth drove loosely to backward point in the West Indian's first over and in his next Ollie Price made a fatal misjudgement when he left a length ball which uprooted his off stump.
Skipper Graeme van Burren and Miles Hammond effected a brief recovery before off-spinner Jack Carson struck with his fifth ball when van Burren missed an attempted pull at one which kept a shade low.
James Coles then got Sussex a sixth wicket in the penultimate over when Tom Price was leg before.
Earlier, Cheteshwar Pujara, John Simpson and Danny Lamb had all passed 50 before Sussex were bowled out for 479 and it was surprising that none went on to make the first hundred of the match.
Pujara eased effortlessly from his overnight 75 to 86 and looked odds on to complete his hundred before gifting his wicket. He drove the ball to deep extra cover and hesitated going for a third run. Sub fielder Jack Taylor's throw was accurate enough to enable Bracey to run him out.
When Fynn Hudson-Prentice was beaten in the flight by Zafar Gohar and smartly stumped Sussex still trailed by 103 runs but Simpson and Lamb tilted the balance in their favour with a measured stand of 143 in 34 overs, beating the previous eighth-wicket county record against Gloucestershire of 122 by George Brann and Walter Andrews which had stood since 1892.
Lamb was the more aggressive, but Simpson, who made a maiden double-hundred against Leicestershire last week, reaching his fifty by lofting Gohar over long on and added eight fours before he misjudged a pull and Hammond ran in from the midwicket boundary to take a fine catch.
Lamb, who scored a century at Leicester, continued his good form with 83 off 116 balls including nine fours and a six. Looking to force the pace, he was bowled by Don Goodman attempting to ramp him over the wicketkeeper.