Sussex 351 for 6 (Haines 133, Coles 78, Zaib 3-61) trail Northamptonshire 371 (Procter 92, Nair 57, Seales 4-86) by

The 25-year-old left-hander - who hit six fifties last season without converting any of them into a century - eased to the tenth first-class hundred of his career as Sussex reached 351 for 6 at stumps on day three, trailing by 20.

They had been in a spot of bother at 94 for 3 but James Coles, who celebrated his 20th birthday last week, embellished his burgeoning reputation with a stylish 78 in a fourth-wicket stand of 137 to go with his three wickets.

Left-arm spinner Saif Zaib checked Sussex's progress by removing both set batters and Sussex captain John Simpson, but in the final hour Fynn Hudson-Prentice and Danny Lamb wrested back the initiative with some aggressive batting, Hudson-Prentice thrashing a 38-ball fifty as they added 93 from 70 balls before bad light intervened with 7.4 overs remaining.

It was Haines' day though. He offered one difficult chance on 107 which was put down by wicketkeeper Lewis McManus diving to his left, but otherwise looked comfortable driving or accumulating steadily off the back foot.

Haines and his new opening partner Tom Clark had launched Sussex's reply with an untroubled stand of 55 before Clark was leg before pushing forward to off-spinner Rob Keogh, who struck again when Tom Alsop missed a delivery down the leg side which went between his legs and Lewis McManus completed an easy stumping.

The persevering Ben Sanderson - the pick of the Northants' attack - knocked back Oli Carter's off stump with a no ball and did so again (this time with a legitimate delivery) two balls later. But with the Kookaburra offering little movement and only gentle turn Haines and Coles turned things around.

Haines pulled Australian Chris Tremain for four to reach his fifty and Coles, demonstrating his strengths through the leg side, was soon into his stride, skipping down the pitch to loft Zaib over long-on for six. He offered a chance on 38 which the diving Bartlett shelled at mid-on but otherwise made serene progress. It wasn't Bartlett's day as deep into the final session he was hit on the helmet by Haines and had to go off.

Haines reached his second hundred against Northants with a single off Sanderson and Coles seemed certain to follow him but both gifted their wickets to Zaib. Coles drove a long hop to mid-on and Haines drilled a full toss to mid-off after facing 183 balls and hitting 19 fours. In between Simpson played on as Zaib collected three wickets in a Championship innings for the first time since 2016.

At the start of the day, Northants added 78 runs in an hour before being dismissed for 371. Sussex made an early breakthrough when Michael Finan drove loosely to extra cover to give Jayden Seales his fourth wicket. He would have had a debut five-for had Jack Carson not put down a regulation chance at fourth slip to reprieve Sanderson when he had yet to score.

It was to prove costly when Sanderson cut loose. He greeted Ollie Robinson by hitting two boundaries off his first over and put on 41 at more than a run a ball for the ninth wicket with McManus.

Robinson eventually got his man when Sanderson (27) top-edged an attempted pull but McManus progressed on to a well-made fifty before he was caught off a top-edge to give left-arm spinner Coles his third wicket. Seales, with 4 for 86, was the pick of the attack but Robinson would have been pleased to get 22 overs under his belt which included seven maidens in his 2 for 67.