Aaron Finch clattered a brilliant 102 not out from 53 balls as Surrey kept alive their slim hopes of reaching the Vitality Blast quarter-finals and severely dented Somerset's, with a six-wicket victory at the Kia Oval.
Somerset started strongly and openers Tom Banton and Babar Azam put on 80 in 8.2 overs - but their challenge fell away dramatically against the spin of Imran Tahir (four wickets for 25 runs) and Gareth Batty (two for 24) and they totalled 157 for nine.
However, Finch's assault emphatically settled matters, with nine sixes helping to bring Surrey their fifth win of the campaign.
They now have 12 points and Somerset, in fourth place with 13, need to beat Middlesex in their final group game on Friday if they are to have a chance of making the last eight.
Somerset chose to bat first in front of a 25,000 sell-out crowd - Surrey's fourth full house in six home games so far - and Banton and Babar gave the visitors a flying start.
Banton's 28-ball 47 was by far the most fluent of the Somerset batting efforts, with leg-side sixes off Sam Curran and Jordan Clark and five fours, the pick of them a reverse flip for four off Tahir in the game's very first over.
Babar hit only three fours, but played his part too in an opening partnership which hinted at an eventual Somerset total of around 200.
Once Banton had fallen in the ninth over, however, the innings lost all its forward momentum. James Hildreth soon followed, stumped off Gareth Batty in the next over for one when he advanced to a well-flighted delivery outside off-stump and yorked himself.
Worse was to come for Somerset, though, with Babar chipping a return catch to Tahir to go for a 31-ball 37 and, in the same 11th over, Ed Byrom (three) also gave the South African leg-spinner a simple caught and bowled off a looping leading edge.
Four wickets had gone in 17 balls, for the addition of only 13 runs, but from 93 for four a mini-recovery was quickly stifled as Batty removed Tom Abell for 14, stumped as he attempted a reverse sweep and Tahir had Roelof Van der Merwe leg before for two.
The lower order did its best to get Somerset up to a defendable total with Tom Lammonby reaching 19 before being caught behind in a nine-ball Jade Dernbach over, the 18th, costing 12 runs.
Clark and Curran grabbed the wickets of Craig Overton and Tim Groenewald in the closing overs and Somerset needed their 10th wicket pair of Jerome Taylor and Max Waller to make sure they batted through their 20-over allocation.
Somerset might still have defended their total if Overton had taken a boundary-edge catch in the eighth over, with Finch on 33, when the Australian pulled a short ball from leg-spinner Waller to deep midwicket and saw the ball bounce through Overton's hands and go over the rope for his fourth six.
Finch did not give any other chances, however, as he followed up that blow, two earlier straight sixes off Groenewald and an opening pulled maximum off Overton, with further sixes off van der Merwe, Waller and two off Lammonby's left arm seamers.
It hardly mattered that Curran had skied Van der Merwe's left arm spin to Abell in the ring, having contributed just nine to a second wicket stand of 61 in a mere 5.1 overs, following Mark Stoneman's departure for 18 to the last ball of the sixth over, or that Ollie Pope was run out for seven in the 15th over.
Finch completed his 52-ball hundred, his seventh in T20 cricket, in the same over with his fifth four - whipped wide of mid-on off Groenewald, and Will Jacks struck successive fours before being caught and bowled for nine by Van der Merwe with just eight more runs wanted.
Clark then hit Taylor into the pavilion for the evening's final six as victory arrived with 3.3 overs to spare.
Bears roar again
A blistering innings of 77 from Ed Pollock guided Birmingham Bears to a seven-wicket victory over Durham via the Duckworth-Lewis method in their Vitality Blast North Group clash at Emirates Riverside.
The Bears were set a challenging total of 153 from 19 overs after rain interrupted the host's innings, with D'Arcy Short top-scoring for Durham with a half-century.
However, Pollock was outstanding on his return to the Birmingham line-up, allowing the visitors to control the tempo of their chase.
The 24-year-old dismantled the Durham bowling attack with ease before he was dismissed for 77.
Matthew Lamb and Will Rhodes saw their side over the line in the final over, lifting them off the bottom of the table, ending Durham's hopes of reaching the quarter-finals of the competition in the process.
The home side were inspired by Bears skipper Jeetan Patel, who put faith in George Garrett to open the bowling on his T20 debut.
He had a first over to forget as Short dispatched him for five boundaries. Chris Green shared the new ball and made the breakthrough with his off-spin, bowling Scott Steel for a duck.
Short and Harry Adair kept Durham moving to reach their fifty in the powerplay, which included a six from Adair that had just enough to clear the rope.
The weather intervened to halt the Durham innings, with play resuming 35 minutes later and the loss of one over.
The two batsmen struggled to find the boundary after the break, although it did not stop them putting a partnership of 70 for the second wicket. Adair tried to attack the spin of Alex Thomson, but could only send a leading edge back to the spinner.
Short worked his way to his half-century from 38 balls - his fourth of the competition. However, a change in ball resulted in his dismissal as Patel turned one through the gate, with the New Zealander narrowly avoiding a front-foot no ball.
Durham needed an injection of pace and it came from their skipper Peter Handscomb scoring a brisk 25, including a six down the ground off Patel, taking his final over for 17 runs.
Graham Clark also played a useful knock of 26, adding late boundaries before he was caught on the fence.
As a result of their striking, Durham surpassed the 150-run mark at the end of their 19 overs, setting Birmingham a competitive total after being adjusted by Duckworth-Lewis method to 153.
Birmingham opened with an attacking intent, putting the pressure on Liam Trevaskis. Pollock and Dominic Sibley scored five boundaries between them from the left-arm spinner's opening two overs.
Pollock continued to provide an early onslaught, dispatching Matty Potts for a six over the leg side and back-to-back boundaries, pushing the run rate above 10 per over.
The home side had no answer for the power of Pollock. James Weighell's introduction into the attack resulted in a 19-run over, including another maximum from the left-hander.
Short broke the opening stand for 83 when Sibley chipped tamely into the deep, but Pollock stayed calm at the other end, reaching his half-century from 24 deliveries.
Short notched his second wicket as Sam Hain played onto his stumps, attempting a reverse sweep. However, Pollock was undeterred and continued to find the boundary, whittling down the total.
Pollock was finally out in the 17th over, smashing a drive straight back to Steel to set up a closer finish than expected. But, Lamb and Rhodes did enough to secure victory with one ball to spare.