North West Thunder 155 for 6 (Lamb 64) beat Central Sparks 119 for 9 (Morris 2-16) by 36 runs
Bethan Ellis and Erin Burns helped pulled the scoring rate back after Thunder had reached 93 for 1 from 11 overs.
But Morris then picked up two wickets with her off spin and proved difficult to score off. She finished with 2 for 16 from her four overs.
It enabled Thunder to follow up their seven-wicket win over Sunrisers at Emirates Old Trafford in impressive fashion.
But Sparks are now facing an upfill task to qualify for finals day – also at New Road on June 10 – after suffering a third successive defeat.
Sparks gave a senior debut to Ellie Anderson who had been part of the England Under-19s side which reached the ICC T20 World Cup final this winter.
Both sides were without players through England commitments in Izzy Wong and Amy Jones (Sparks) and Sophie Ecclestone and Kate Cross (Thunder).
Sparks captain Eve Jones won the toss and put The Thunder into bat and Katie George made an immediate impact with the new ball.
Liberty Heap mistimed a drive and Bethan Ellis took a fine low catch stretching forward at cover.
Lamb was joined by Morris and the pair scored freely in lifting the total to 55 for one by the end of the powerplay.
Lamb struck the first six of the innings off Hannah Baker over long on.
The stand was worth 91 in 10.5 overs when Morris (36) aimed a reverse sweep at Bethan Ellis and perished at backward point.
Lab completed an excellent 40-ball half-century but her dismissal – caught off a skier by keeper Abbey Freeborn also off Ellis for 64 – saw the innings lose momentum.
Erin Burns accounted for Deandra Dottin, who holed out to deep mid wicket, and Ellie Threlkeld, bowled behind her legs sweeping, in the same over.
With Seren Smale stumped off Baker in the final over, the last nine overs produced just 62 runs for the loss of five wickets.
Sparks made the worst possible start in reply when skipper Jones edged an away swinger from Mahika Gaur to the first ball of the innings and was caught behind.
It became three for two when Ellis attempted a second run after turning Tara Norris to deep mid wicket and was run out by Morris’ throw to keeper Threlkeld.
Davina Perrin and Burns batted sensibly in adding 52 in seven overs before the former went lbw in Naomi Dattani’s first over.
Burns started to accelerate and clubbed Steph Butler for a maximum over midwicket.
She raced to 41 off 23 deliveries but then top-edged a return catch to Morris who in the same over had Abbey Freeborn lbw.
Three wickets fell in an over from Norris, including a run out, to seal Sparks fate
Source: ESPN Crickinfo