Sussex's unbeaten Championship record, which stretches back nearly three months, is under threat from second division leaders Northamptonshire.

The hosts moved into a strong position after two days of the first versus second contest at Wantage Road thanks to Russell Warren's first century of the season and only his second in the last three years.

The tall right-hander made 113 not out, sharing an unbroken fifth-wicket stand of 188 with all-rounder Tony Penberthy who resumes this morning in sight of his first century of the season.

By the close Northants had reached 327-4, a lead of 95 with power to add this morning.

Sussex had enjoyed parity in the first half of the day, removing Northants' top four for 136 before Warren and Penberthy took full advantage of ideal batting conditions to break the county's 80-year-old record for the fifth wicket against Sussex.

Chris Adams tried everything to break the stranglehold, switching around his two slow bowlers and even coming on himself for a five over spell after tea.

But once Warren and Penberthy had played themselves in, they batted with increasing freedom as Sussex's bowlers struggled to get much joy from a flat pitch where the ball came on to the bat at a nice height all day.

Umer Rashid was the pick of the Sussex attack.

The left-arm spinner came on in the sixth over and maintained admirable control in three lengthy spells, the first of which brought him 1-24 from 16 overs with seven maidens.

His sole success came in his sixth over when Adrian Rollins got the faintest of edges to wicketkeeper Nick Wilton as he propped forward.

Varying his line of attack and flight intelligently, he should have been celebrating again in the 63rd over when Penberthy, who had made 11, was badly dropped at silly point by the normally reliable Adams who spilled the ball after three desperate attempts to hang on to a bat-pad offering.

If that catch had gone to hand Sussex may have been able to restrict the leaders' advantage to manageable proportions.

Instead Warren and Penberthy sailed serenely on. Warren offered one difficult chance to square leg early in his innings, but he drove and cut with impressive authority before reaching his century after spending 20 balls on 98 with a meaty pull off Jason Lewry in the second over with the new ball.

It was his 15th boundary and he'd added two more by the close while at the other end Penberthy seemed to feed off his partner's confident approach after a cautious start.

The Cornish born left-hander pulled Rashid contempteously over mid-wicket for six after tea and by the close was eight short of his hundred, having also hit ten boundaries and passed 5,000 career runs in the process.

Earlier James Kirtley had taken his tally of Championship wickets to 45, 26 of which have come in the last four matches, by removing Matthew Hayden and Mal Loye in an impressive opening spell.

Hayden would have been disappointed to guide a ball which swung late straight to square leg while Loye, who had crashed the previous two deliveries to the mid-wicket boundary, fell leg before when Kirtley pitched the next ball up.

Warren and South African Jimmy Cook had repaired the early damage in a stand of 60 in 25 overs for the fourth wicket when Cook mis-timed a drive straight to cover to give Justin Bates his first Championship wicket for two months.

Bates was tidy enough, but it's fair to say that he lacked the variation shown by the two Northants off-spinners, Jason Brown and Graeme Swann, when they took six wickets between them on the first day.

How Sussex fare against them when they bat again at some stage today will be crucial to their hopes of saving the game.