Matt Prior's magnificent 133 not out at Hove yesterday could not stop Sussex from surrendering their proud unbeaten home record.

They last tasted Championship defeat in the final game of 2004 against Surrey 26 matches ago but Durham thoroughly deserved the victory which will infuse them with the belief that they can win the title for the first time.

Sussex's hopes of making it a hat-trick could largely depend on how many of their fragile-looking top order batsmen can rediscover some form.

The top three - Chris Nash, Carl Hopkinson and Mike Yardy - have all shown glimpses of their best in the six matches so far but have lacked consistency.

Between them they have scored one Championship hundred since the start of last season and Sussex are missing Richard Montgomerie's adhesive qualities more than they might have expected.

Skipper Chris Adams, who should return after injury at Canterbury on Friday, is averaging a modest 22 while Luke Wright failed to make the most of promotion up to No.6 against Durham.

Sussex have built their successes since 2003 on their ability to take 20 wickets and, even though Mushtaq Ahmed is still searching for rhythm after knee surgery, the attack is getting back to its best with Jason Lewry and Corey Collymore offering a potent new-ball threat.

But they need runs on the board first and so far Sussex have only once got past 350 in an innings this season. Opponents sense that the champions are vulnerable.

Rory Hamilton-Brown made an encouraging half-century on debut against Durham and the fact that two second-team games have been completely washed out has not helped fringe players looking to make an impression.

Apart from Adams' return, it would be a surprise if there were any changes for the Kent game. Perhaps there should be. Coach Mark Robinson's patience is not inexhaustable and some individuals will be playing for their places at Canterbury later this week.

Prior is not one of them. He has scored 615 Championship runs - more than anyone else - after lodging his third hundred of the season and the 18th of his career.

The quality of his hitting almost, but not quite, upstaged Steve Harmison whose hat-trick set up Durham's ultimately comfortable eight-wicket win.

If acting captain Prior made one mistake it came at the toss. The forecast, which suggested cloudy skies on days one and three, was accurate and it meant Sussex were always batting in the worst conditions.

They quickly lost Yardy yesterday and only cleared their 87 runs deficit in the last over before lunch when Prior and Murray Goodwin dug in. Goodwin was unusually circumspect but it had been desperately hard work in murky light, particularly against Harmison who once again generated extravagent lift down the slope.

Goodwin had faced 117 balls when he fell for the second time in the match to Callum Thorp and Wright departed for a second-ball duck in the same over, squirting a catch to cover as he aimed towards square leg.

At that stage Sussex's lead was just 26 and their position seemed hopeless when Harmison returned to take the second hat-trick of his career with the first three balls of his second spell.

Hamilton-Brown edged an ambitious drive, Robin Martin-Jenkins nicked one playing defensively and Mushtaq's off stump was sent cartwheeling by a yorker while a bemused Prior, who was on 72, looked on from the other end.

With only Corey Collymore and Jason Lewry left, Prior had licence to play some shots and in the next 45 minutes he treated the crowd to some exhilarating strokeplay.

Even Harmison was made to look mortal as Prior went from 50 to 100 from just 44 balls with all but six of those runs coming in boundaries. They included successive sixes off Harmison, carved off the back foot over backward point and third man, which took him from 92 to 104. The front-foot drive off the same bowler which comfortably cleared long off was an even better blow.

In ten overs he smashed 55 runs as the last two wickets put on 74 and the only pity was that both his partners were run out taking unneccessary risks trying to give Prior the strike. Collymore and Lewry had arguably both shown more application than some of their team-mates up the order.

The crowd generously acclaimed Prior's highest score of the season - made off 138 balls with 16 fours and five sixes - and they even sensed an unlikely Sussex win when Lewry removed stand-in opener Phil Mustard and Will Smith with the new ball as Durham chased a target 126.

But Michael Di Venuto's stylish 60 secured only Durham's second ever win on Sussex soil.

Is it time for changes to the batting line-up?