Yorkshire 165 for 3 (Willey 79, Lyth 66) beat Northants 162 for 8 (Cobb 68*, Willey 3-30) by seven wickets
David Willey and Adam Lyth delivered a crushing seven-wicket win for Yorkshire with over four overs to spare at Northamptonshire to keep the White Rose on course for the Vitality Blast quarter-finals.
Set 163, Willey and Lyth shared 150 for the second wicket in 80 balls. Neither could see Yorkshire over the line as Willey fell for 79 from 44 balls and Lyth 66 in 41 but the damage was done as the visitors won with 27 balls to spare.
Yorkshire now face Nottinghamshire in their final game at Headingley knowing victory will guarantee their place in the last four.
Josh Cobb was the only batsman to show for Northants with 68 not out as the home side posted 162 for 8 having won the toss but not for the first time in the competition, the Northants' attack struggled as Lyth and Willey hammered the bowling around Wantage Road.
Lyth got down one knee to slog-sweep Ben Sanderson for six before taking 22 from the fifth over of the innings bowled by Richard Gleeson. He advanced down the wicket to lift a six then four over extra-cover, carved four over point, glanced another boundary past the wicketkeeper before driving four more past mid-on. It ensured Yorkshire raced to 74 in the Powerply for the loss of Tom Kohler-Cadmore caught at point first ball.
Having passed fifty in 26 balls, Lyth again went down on one knee to this time slog-sweep Luke Procter for six but trying to finish the game, miscued a drive to extra-cover.
Willey was again in great touch against his old county. He flashed his opening boundary off the back foot past extra-cover, pulled Hutton over deep-square for six and sliced Sanderson over point. He swung Cobb's off-spin over long-on for six more and struck a third six down the ground off Seekkuge Prasanna.
Yorkshire were cruising at 113 for 1 after 11 overs and Willey slogged Brett Hutton for consecutive sixes before slog-sweeping Graeme White for another maximum in an over that cost 21. But he pulled Sanderson to deep midwicket shortly before Gary Balance struck the winning runs.
Yorkshire were on top from the start as Matt Fisher removed both Northants openers in his first over both for 16 and both to leading edges. With his first ball, Charlie Thurston edged to third man where Kane Williamson ran in to take a smart catch and with the final ball of the over, Ben Duckett edged to backward point where Lyth leapt above his head. The wickets ensured it was Yorkshire's Powerplay as Northants reached 35 for 2.
Cobb drove his opening boundary past extra-cover but then pulled off a top-edge perfectly between the wicketkeeper running back and long leg running in. At 50 for 2 after eight overs, Northants were bumping along and Cobb cleared his front leg to smash Tim Bresnan's first ball over deep midwicket and, as Bresnan went too full, struck a second six over long-on as the home side reached the half-way point at 72 for 2.
Alex Wakely, after a patient start, flicked Liam Plunkett wide of midwicket for four but chipped the same bowler later in the same over to mid-on to fall for 14. Steven Crook arrived and immediately struck both Lyth and then Plunkett straight down the ground for six, edged Plunkett for four but holed out to deep cover for 18. And when Prasanna swung and missed at a Jack Brooks slower ball and lost his leg stump, Northants were 106 for 5 in the 15th over.
Cobb pulled Bresnan for four wide of long-on before heaving Willey for consecutive sixes out of the ground to pass fifty in 32 balls. He opened the blade to steer Bresnan for four to begin the 18th over which cost 16.
But just when Northants had built some momentum, Willey bowled an extraordinary triple-wicket maiden in the 19th over. He had Procter caught behind and then White caught at deep square next ball before Hutton hooked at the fifth delivery and gloved it behind. Two sixes in the final over boosted the Northants total but it was nowhere near enough.