Durham Jets moved back to the top of the Vitality Blast North Group courtesy of a 14-run win over the Leicestershire Foxes at Emirates Riverside.
Durham battled their way to a total of 156 from their 20 overs on a slow wicket thanks to a half-century from captain Tom Latham, while James Weighell provided late impetus with three sixes.
Leicestershire struggled from the off, losing five early wickets. Colin Ackermann did his utmost to keep his side in contention with 74 - but it proved to be in vain as the Jets closed out the win to move within touching distance of a quarter-final berth.
Durham won the toss and elected to bat - and Latham and Clark ensured that their side once again made a solid start.
The home side approached 50 before the powerplay before Zak Chappell produced a fine delivery to bowl Clark for 23, then Paul Collingwood lasted just two balls and was run out by Gavin Griffiths going for an ambitious second.
The Jets continued to struggle to time the ball off the middle of the bat. The hero of their win over Lancashire Liam Trevaskis had a tough time, scoring eight off 12 before being stumped off Mohammad Nabi.
Latham made a solid half-century but was forced to work hard for his runs, reaching the milestone in 45 deliveries.
The New Zealander fell for 52 to Callum Parkinson, being bowled attempting a reverse sweep.
Will Smith kept the scoreboard ticking off with a decent knock of 26 but the spark was provided by Weighell late in the innings, with the left-hander crashing three sixes over the rope to take Durham over the 150-run mark.
Weighell was run out off the penultimate ball - but Ryan Davies scampered a three off the final delivery to reach 156.
Leicestershire's reply got off to a poor start against the off-spin of Smith. Neil Dexter miscued his drive straight to Weighell, while Ben Raine followed to Chris Rushworth's first ball, edging to Collingwood at slip.
Nathan Rimmington compounded the Jets' advantage, bowling Mark Cosgrove for seven before having Ateeq Javid caught behind to leave the visitors 22 for four in the fifth over.
Nabi fell to the leg-spin of Ben Whitehead to continue the procession of Leicestershire wickets, before Foxes skipper Ackermann offered resistance, playing a well-crafted innings to reach his half-century off just 36 deliveries.
He combined with Ned Eckersley to reach a partnership worth 50 in 40 balls to keep the visitors in contention - although the run rate continued to climb despite their efforts.
Leicestershire's captain fell five short of his career best for 74 in the penultimate over to Rimmington, who claimed his third wicket.
Chappell had a late dart, but the Jets were able to close out the victory by 14 runs.
Another brilliant display of power hitting by Josh Cobb gave Northamptonshire a first Vitality Blast win and dented Derbyshire's quarter-final hopes at Derby.
Cobb followed his century against Birmingham Bears with an explosive unbeaten 73, including seven sixes, off 37 balls as the visitors chased down a target of 178 with 10 balls to spare.
Billy Godleman had made a T20 best 77 from 55 balls as the Falcons posted 177 for six - but Cobb destroyed their attack to finally give the Steelbacks victory after nine defeats and a tie.
There was no sign of what was to come when the Falcons started slowly after winning the toss as the seamers found plenty of movement on a grassy pitch, with only 41 runs coming from the powerplay.
Calum MacLeod was caught in the third over at the second attempt at slip off Rory Kleinveldt, who then struck Anuj Dal a painful blow on the right hand with a venomous delivery.
Dal was beaten by a ball from Nathan Buck that came back sharply and although Wahab Riaz pulled a low full toss from Brett Hutton for six, he was run out off the next ball by a direct hit from cover.
At the halfway stage, the Falcons were 70 for three but Godleman drove Seekkuge Prasanna for six over long-off, while Madsen cut and pulled Buck for four consecutive fours in the 13th over.
Godleman completed his 50 from 43 balls and then launched the next delivery from Prasanna over long-on but Madsen drove a slower ball from Ben Sanderson to cover to break a stand of 83 from 49 balls in the 16th over.
Godleman was run out going for a second but Gary Wilson provided late acceleration by pulling Kleinveldt for six in an unbeaten 24 before Buck restricted the Falcons to three off a clever last over.
Northamptonshire's reply started well with Ricardo Vasconcelos ramping Lockie Ferguson for six, while Ben Duckett drove and pulled powerfully as the Steelbacks took 62 from the powerplay.
Duckett was threatening to take control when he missed a reverse sweep at Alex Hughes and Ferguson delivered a searing yorker to knock over Ricardo Vasconcelos in the ninth over.
Cobb showed he was in the groove with a top-edged six and a straight-driven four off Hardus Viljoen, before taking another six off Hughes.
Ben Curran, brother of Surrey's Tom and Sam, made only two on his senior debut but Cobb pulled Hughes for six before twice driving Viljoen over the ropes as he surged to a 27-ball 50.
Northamptonshire needed only 20 off the last three overs and - with skipper Alex Wakely lending sound support - Cobb finished it in style with consecutive sixes off Ravi Rampaul.
Johann Myburgh thumped an unbeaten 54 to keep Somerset top of the Vitality Blast South Group with a six-wicket win over Hampshire.
Opening batsman Myburgh, who began his county career at Hampshire, announced earlier this week he would retire from the game at the end of the season.
And the decision to quit might have been made prematurely as he clinically smashed the ball around the Ageas Bowl to chase down 129 with seven balls to spare.
Hampshire toiled in making 129 for eight but where the hosts had struggled, Myburgh appeared to find the going much easier as he stroked boundaries at will.
He added 32 for the first wicket with Steven Davies, who was brilliantly caught in the covers by a diving Liam Dawson.
Myburgh was unfazed by the loss of Davies as he got his head down and kept the run rate ticking at just above the six an over needed.
Peter Trego was deceived by a Mujeeb Ur Rahman variation, as he played on, and James Hildreth hit straight up in the air to be caught by wicketkeeper
Tom Alsop, but Myburgh remained comfortable.
Myburgh moved to his 11th T20 fifty and although Dawson had Corey Anderson lbw, eased Somerset home.
Lewis Gregory won the toss and elected to bowl on the same wicket that was used for the earlier Southern Vipers and Yorkshire Diamonds game.
Hampshire never got to grips with the pitch though, despite James Vince firmly cutting Max Waller through point first ball and Rilee Rossouw dispatching a six over cow corner.
That was as good as it got for the hosts as the wickets fell with regularity.
Rossouw dragged a full ball to mid-wicket, before Jerome Taylor found Vince's leading edge, with Tom Abell completing the catch at backward point.
Hampshire were left on 45 for two at the end of the powerplay and quickly lost Alsop skying to mid-wicket and Dawson offering up a simple catch at point.
Sam Northeast attempted to anchor an end - scoring 30 off 36 balls - but nobody else could build around him.
The former Kent batsman eventually fell off a top edge, which Hildreth easily caught at short fine leg, before Joe Weatherly was bowled.
Chris Wood holed out to long on and Gareth Berg was bowled as Taylor claimed three for 39.