Stunning hitting by Aaron Finch and Jason Roy saw Surrey cruise to a remarkable nine-wicket win over Middlesex in the Vitality Blast as they chased down a target of 221 with four overs remaining.
Australia batsman Finch finished on 117 not out from 52 balls, while England opener Roy made 84 from only 37 deliveries before holing out in the 14th over at the Oval.
Paul Stirling's spectacular 58-ball 109 for Middlesex was overshadowed as Finch and Roy plundered an astonishing 194 for Surrey's first wicket - scoring 98 in the initial six-over powerplay alone - to spearhead a victory achieved with a barely believable 24 balls to spare.
Johann Myburgh also reached three figures to fire Somerset to a resounding 10-wicket win over Essex.
Myburgh plundered an unbeaten 103 off 44 balls, which included three sixes and 16 fours, as Somerset knocked off Essex's modest 135 for nine inside 12 overs.
Tom Banton finished 29 not out while Jamie Overton and Jerome Taylor did the damage with the ball, taking three wickets apiece.
Kent, who had briefly been replaced by Somerset at the top of the South Group, returned to first place after bowling Hampshire out for just 88 to seal a 51-run win.
Marcus Stoinis took four for 17 and Adam Milne recorded three for 14 to rescue their side after posting what appeared to be a below-par 139 for seven.
Yorkshire strengthened their grip on a quarter-final place as Kane Williamson guided them to a six-wicket win over Northamptonshire.
The New Zealand captain scored an unbeaten 54 off 44 balls as the Vikings overhauled their visitors' total of 129 for seven.
A savage innings of 86 not out in only 32 balls by Afghanistan all-rounder Mohammad Nabi secured a five-wicket victory for Leicestershire against Lancashire.
Coming to the wicket with his side on 92 for five in the 11th over and needing another 99 runs to win, Nabi tore the Lancashire attack apart, hitting eight sixes and four fours as the visitors cruised home with eight balls to spare.
Alex Davies had earlier made a career-best 94 not out in the home side's 190 for five but it was not enough.
Timm van der Gugten held his nerve as Glamorgan earned a two-run win over Gloucestershire.
Chasing 202, Gloucestershire went into the final over needing 16 to win and after Andrew Tye hit two sixes it was on, but the Dutchman won it for Glamorgan when he bowled Tye off the final delivery.
Ross Whiteley smashed 60 off 26 balls as Worcestershire gained a dramatic three-wicket win over Durham.
The all-rounder rescued a game which appeared to be heading in the Jets' favour after Tom Latham had hit 78 of their 194 for seven.
Ian Bell wrote his name in the record books but finished on the losing side as Birmingham fell to a 16-run defeat against Derbyshire.
Bell passed Jonathan Trott's total of 1,911 runs to become the Bears' highest run scorer in T20 cricket but his 65 from 51 balls was not enough as the visitors came up short chasing 144.