YORKSHIRE'S hopes of a one-day treble were wrecked as much by their own over-ambition as by Durham last night.

Both were left with two wins from five group games in the Twenty20 Cup and the seven-wicket defeat brought further Riverside frustration for Yorkshire after Sunday's totesport League washout.

They can still win promotion in the one-day league and have tomorrow's C & G Trophy semi-final at Bristol to look forward to, but they are out of the Twenty20.

Because Durham have permission to start their matches at 6pm the danger of the light fading meant Yorkshire wanted to bat first. But under the pressure of having to improve their run rate in order to have a chance of progressing to the quarter-finals they faced the difficulty of deciding how many they could realistically expect to score. They were guilty of going for their shots as they might on faster surfaces at Headingley and slumped to 55 for six before settling down to reach 126 for seven.

It was more than Durham had managed when batting first in their two previous Twenty20 home games, but they seemed to benefit from knowing what they had to do and from the return after injury of Marcus North. He put on 44 for the first wicket with Phil Mustard, who went on to make 42 off 34 balls, leaving Gary Pratt and Gareth Breese to steer Durham home with ten balls to spare.

Breese hit two sixes in an over off Andy Gray in reaching 24 off 16 balls and Pratt made 35 not out at a run-a-ball. Durham took advantage of England making Stephen Harmison available to hand the paceman his Twenty20 debut at the expense of Graham Onions, while North replaced Ian Pattison. But Zimbabwean Andy Blignaut is waiting until Sunday's totesport League game at home to Middlesex to make his debut.

Yorkshire might have felt there was a conspiracy as they had to face Andrew Flintoff and James Anderson in Wednesday's Roses clash, then Harmison last night, while they have to wait until tomorrow's C & G semi-final to include Michael Vaughan.

There was a warm reception for Harmison from the 5,700 crowd in the first of what is likely to be only two appearances for Durham this season. But as with most Riverside pitches, the surface was too slow to suit him, which also meant Yorkshire were not going to repeat their high scoring feats of earlier games.

Yorkshire brought in Chris Silverwood for Steve Kirby and Vic Craven for skipper Craig White, who will receive the results of a scan on his injured knee today. But there is a fear that he could be out for the season. Acting captain Matthew Wood won the toss and went in to open with Wednesday's match-winner Ian Harvey, who guided Harmison's opening delivery through gully for a single.

The third ball was a bouncer, which was called no-ball as it flew through well above shoulder height, but there were no more runs off the over. The second over, however, yielded 16 as the usually miserly Neil Killeen was pulled through mid-wicket and picked up behind square for boundaries by Harvey and also sent a ball down leg side for four wides.

Harvey had all the time in the world to work Harmison off the back foot through square leg for his third four, only to fall for 14 to the next ball. The paceman showed he can combine brain with brawn by bowling a slower yorker-length ball, which hit leg stump after Harvey tried to turn it to mid-wicket. Harmison was jubilant, and so were his team-mates.

Only one run was added before it became 24 for two when Wood drove Killeen tamely to mid-on, then Anthony McGrath pushed forward in Killeen's next over and edged to Andrew Pratt. Standing up to the stumps, the wicketkeeper took a comfortable catch.

Harmison bowled two wides in his third over but the Yorkshire procession continued when he was replaced by Graeme Bridge and Michael Lumb went down the pitch and was stumped.

When Phil Jaques fell for 12 in the left-arm spinner's second over, brilliantly caught by a leaping Gordon Muchall at long-on, it was obvious that Yorkshire were being over-ambitious. Their first priority was to win the game rather than worrying about run-rate, and a glance at previous scores at Riverside would have told them that 140 should be enough. When Tim Bresnan played back to Mark Davies and had his off bail trimmed by one which left him Yorkshire were 55 for six in the tenth over.

They were fortunate to have the experienced Richard Blakey coming in to steady the ship, but it was left-hander Craven who kept the score moving by cutting Breese for four and reverse sweeping Bridge to the fine leg boundary.

At 95 for six with four overs left Harmison returned for his one remaining over, which cost only five runs to leave him with one for 19.

Blakey, scoring mainly from the sweep, perfectly bisected the two men on the boundary as ten came off Breese in the 18th over.

But in trying to maintain the momentum Blakey miscued Davies to mid-off with ten balls left after contributing 18 to the stand of 56 in nine overs. Killeen's first two balls of the final over were yorker length just outside off stump and Craven missed them both, but he then hit a slower, straighter ball wide of long-on for the only six of the innings. Yorkshire had hit 22 sixes in their four previous games, but Riverside matches have produced no more than two a game.

Two byes and two more runs came off the final over, leaving Craven on 44 not out off 47 balls and Killeen in the unusual position of being Durham's most expensive bowler with two for 35. Davies was the most economical with two for 14. Bresnan conceded only four of the first over of Durham's innings but then misfielded at third man to give North a four off Silverwood.

Mustard pulled Bresnan to the boundary in the third over then sent a drive off Silverwood into orbit over mid-on. Richard Dawson raced from mid-off to dive and get both hands to the ball but could only tip it towards the rope.

North followed up with two leg-side fours as 15 came off the over, giving Durham their best opening stand of the season in this competition. Mustard smashed Bresnan first bounce over the rope at long-on and at 41 after five overs Yorkshire needed a tight over. Silverwood obliged as, despite bowling a wide, he conceded only two singles.

Off-spinner Dawson, who had a nine-wicket match haul in the championship clash at Riverside last month, came on for the seventh over and struck with his first ball.

North went for a sweep and was lbw for 20 and four balls later Andrew Pratt was run out for one when Andy Gray hit the stumps from backward point.

Only four singles came off Silverwood's final over and only one off the next three balls from Dawson. But Mustard then launched a superbly-struck six over long-on and collected a couple of twos to put Durham back ahead of the clock.

With the total on 86 in the 13th over Mustard lofted an easy catch off Gray to mid-wicket, but Breese looked much more comfortable at No 5 than he had at three and there was nothing Yorkshire could do to stem the flow.

Gary Pratt survived a sharp chance to McGrath at backward point on 26, but once Breese had driven Gray over long-on then lifted him high into the crowd over mid-wicket in the 17th it was a simple stroll for Durham.