Berg & Sanderson sound more like a high-end headphones manufacturer than a lethal new-ball partnership, and the very mention of their names has been enough to leave Sussex supporters' ears ringing this month. After sharing 19 wickets in the reverse fixture at Wantage Road they have managed another nine between them in the Hove sunshine this week, but it was their 51-run stand for the last wicket that maintained Northamptonshire's advantage on the second day.

Saif Zaib had held their response to Sussex's 175 together with a determined half-century, adding 53 with Adam Rossington after George Garton cleaned up Simon Kerrigan early on, but when he edged behind shortly after lunch the lead was only 30. Sussex hoped they would be comfortably in front by teatime, but hadn't counted on Berg's long-handled bludgeoning: he cut and pulled the seamers confidently, and dumped Jack Carson over the hospitality tents for a six that had sunbathers taking cover on the seafront.

Still going strong at the age of 40 (and why shouldn't he be, when Darren Stevens is around), Berg's performances this season have made Middlesex's decision to release him in 2014 - fearing he wouldn't recover from a shoulder injury - look bafflingly premature. He now combines his playing duties with a player-coach role for Italy's national team, and has aspirations to recruit Jade Dernbach after securing Grant Stewart's services for the European leg of T20 World Cup qualifying this autumn; on days like this, he must surely reflect that la vita è bella.

Berg was a spot lower than usual at No. 10 thanks to Kerrigan's nightwatchman duties, but was a handy No. 7 for much of his first-class career and has clearly not lost the knack - though was dropped at second slip before he had got going. Sanderson, by contrast, has no pedigree with the bat but was happy to tuck in when Garton missed his length with the new ball. Their stand ended when his stumps were rearranged by the same bowler, but not before the lead had crept up to 81, securing a second batting bonus point that may yet prove vital in their bid for a top-two finish.

In the absence of Ollie Robinson, who left the ground to a round of applause from the returning fans on Thursday before joining up with England's Test squad, Garton is the senior citizen in Sussex's attack at the wizened age of 24, some four years older than their three other frontline bowlers. He is still relatively raw in red-ball cricket, with a career economy rate above four an over, but it is an impressive sight when he lets rip and lands one where he wants, generally leaving stumps splattered.

Sussex are considering resting Garton for next week's fixture at Headingley with an eye on the T20 Blast, but Jamie Atkins and Henry Crocombe - both 19-year-olds - showed enough control to suggest they will cope in his absence: Atkins bowls brisk outswingers with a tennis-style grunt on release, while Crocombe has a more classical action and finds good bounce thanks to his height.

Berg and Sanderson both made breakthroughs in Sussex's second innings - Tom Clark's hard-handed push nestling in Ben Curran's hands at third slip, and Aaron Thomason nicking through to Ben Brown - but they were largely blunted by an impressive knock from Tom Haines, who passed 50 for the fifth time this season and is the leading run-scorer in Group Three.

Haines is only 22, but is already the fourth-most experienced player in this side in terms of first-class appearances. His early promotion to the first team under Jason Gillespie means that his overall record - an average of 30.76 - is underwhelming, but he has been the standout batter in a top order featuring two Test players on overseas contracts.

He was particularly strong when Northants' seamers dropped short, and recognised that with the pitch only offering movement when the ball is new, playing his shots to take the shine off was the way to go. He raced to 41 off 42 balls and despite some dicey moments during a probing Sanderson spell after tea, survived until the close with Brown - who cut with characteristic disdain for the short ball - in an unbroken 44-run stand.

Haines is one of six left-handers in Sussex's top eight, and the presence of some footholes outside their off stump when spinners bowl from the Sea End may yet prove crucial. Kerrigan, who had struggled for rhythm in the first innings, used them to his benefit as some balls turned sharply while others skidded on in a tight spell after tea, with Northants applying the squeeze.

He took wickets in successive overs when Stiaan van Zyl chipped back a half-volley and Travis Head's tentative prod was well taken by Ricardo Vasconcelos at slip, and he should have had three in seven balls if Vasconcelos had clung on when Clark edged his first. That left Sussex two runs behind and three wickets down, and when Clark fell to Berg they were effectively 17 for 4. Their lead heading into the third day is slender; the usual pairing's first spells in the morning will go a long way to determining the outcome.