Royal London One-Day Cup Group A at New Road.
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Ian Cockbain booked Gloucestershire's place in the Royal London One-Day Cup quarter-finals after escaping from an early ambush by Worcestershire paceman Mitchell McClenaghan at New Road.
The New Zealander took two wickets in five balls as the West Countrymen stumbled to 10 for three but a rain hold-up allowed them to regroup before Cockbain's unbeaten 98 secured a five-wicket win with 17 balls to spare.
Worcestershire, who still have a slim chance of reaching the knockout stage, disappointingly folded for 229 after looking well set with 89 from Tom Fell and 80 by Alexei Kervezee.
Rain during the interval brought Duckworth-Lewis calculations into play. The target became 216 in 43 overs and a further revision to 214 from 41 followed a second, shorter break after McClenaghan's damaging intervention.
Cockbain brought some composure to a critical situation and Gloucestershire were able to recover from losing Michael Klinger and Chris Dent to catches behind the wicket in McClenaghan's first over.
Hamish Marshall also fell cheaply, pulling Jack Shantry to mid-wicket, but Cockbain and Gareth Roderick blunted Worcestershire's seam-reliant attack in a partnership of 64 in 12 overs.
When Roderick was bowled for 28 by one that kept low from Shantry, the impressive Will Gidman stepped in by adding 44 from 40 balls to his bowling return of four for 41.
The all-rounder was caught at deep square-leg as McClenaghan finished with three for 46 but Gidman's brother Alex made 28 not out in escorting to Cockbain to a personal-best one-day score with 13 fours, mostly from stylish drives.
Worcestershire's innings was heavily based on a single partnership and then disintegrated so badly that the last eight wickets - half of them taken by Gidman - crashed for the addition of 58 runs.
Kervezee and Fell seemed to be in cruise control, having put on 159 in 31 overs together, until a breakthrough by Craig Miles dramatically shifted the balance of power.
Kervezee fell under edging to wicketkeeper Roderick, but it should not have been a reason for his team to go into freefall.
Ross Whiteley's innings seemed to symptomise a sudden outbreak of uncertainty. Having blocked almost everything in making a single from 14 balls, he launched a six off Jack Taylor and then went for 12, well caught on the boundary edge by Benny Howell.
That was the first of Gidman's wickets and even then the damage would have been manageable if Fell had been able to bat through. Instead he went for the big shot and drove off-spinner Taylor straight to Cockbain at long-off.
Gloucestershire's tight bowling and keen fielding was too much for the lower order. The innings contained only 24 boundaries, all bar five of those coming when Fell and Kervezee seemed to have done all the hard work in correcting Worcestershire's sluggish start.
The first power play yielded only 26 runs in 10 overs for the loss of the openers, Daryl Mitchell playing on to David Payne and Tom Kohler-Cadmore running himself out.
Gloucestershire captain Klinger said: "We don't want to let up now. We are in the quarter-finals but we want a home draw.
"We play Derbyshire in our last game and because Yorkshire play Essex, it is in our own hands. We would love a quarter-final in front of a big crowd at Bristol."
Worcestershire assistant coach Matt Mason added: "We were in a fantastic position to get 300 again and then unfortunately there were some poor decisions by our batsmen. Shot selection was questionable at best.
"As a result we left our bowlers with too much to do."