Yorkshire 132 for 4 (Williamson 52*) beat Northamptonshire 129 for 7 (Thurston 41) by six wickets
Yorkshire tightened their grip on a quarter-final place in the Vitality Blast with a routine six-wicket victory over winless Northamptonshire at Headingley.
The Vikings cruised past the Steelbacks, who were hesitant in posting 129 for 7 before failing to defend it, despite Richard Gleeson getting Adam Lyth caught behind after two balls.
Yorkshire have now won six of their 10 games and sit inside the top four of a hugely competitive North Group table on 12 points.
While they still have work to do to qualify, they are definitely on course ahead of Thursday's sold out Roses clash here against Lancashire.
Debutant Charlie Thurston top-scored with 41 for a Northants side who have now lost eight of nine matches. The other was tied.
The Vikings fell to 22 for 2 inside five overs of the chase, but Kane Williamson steered the ship with an unbeaten 52 not out off 44 balls, including two sixes. They won with eight balls remaining.
After electing to bat, Northants were tied down as Yorkshire's quartet of seamers - David Willey, Jack Brooks, Steve Patterson and Jordan Thompson - all bowled tidily to restrict the score to 35 for 2 after seven overs, when spin was introduced.
Brooks had a hand in the two wickets to fall, quite literally, as the score slipped to 16 for two in the fourth. He had Richard Levi caught behind and deflected a Ben Duckett straight drive onto the stumps at the non-striker's end to run out Josh Cobb.
Thompson then claimed the important scalp of Duckett in the ninth over as the left-hander miscued to mid-off, leaving the score at 48 for 3.
It was soon 62 for 4 when Steven Crook fell in similar fashion to Duckett, this time off Patterson's bowling in the eleventh.
Thurston pulled his third ball for six off Patterson, but it was brief respite for the Steelbacks as captain Alex Wakely holed out to long-off as Azeem Rafiq struck.
Willey and Patterson again struck late on, the latter getting Thurston caught at deep cover in the last over, as each member of Yorkshire's five-man attack struck.
Willey was the pick with 1 for 20 from four overs, while Patterson returned 2 for 26.
The hosts caught well and fielded brilliantly, with a highlight of the Northants innings being when Yorkshire mascot Vinny the Viking played his part in tackling a pitch invader.
After Gleeson had Lyth and Willey was run out going for two, Tom Kohler-Cadmore and Williamson took the sting out of the situation against an accurate attack.
The former then skied Seekkuge Prasanna's leg-spin to long-off in the 10th before Williamson and Gary Ballance found the gaps and accumulated in a 51-stand before the latter fell to Gleeson late on.
Williamson reached a second successive fifty off 42 balls with his second six in the 18th over and helped to finish the game in the next.
Northants did increase the asking rate to seven runs per over for the last seven, but it never looked like being their night even though runs did not flow for either side.