The Lancashire all-rounder made 58, took 4-13 and pouched an important catch as the visitors secured a 12-run victory at Emerald Headingley, restricting the home side to 106-9 in reply to 118-6.
Lamb said: “I got a good start to my innings and just wanted to stay in. It wasn’t an easy pitch – it was a bit stoppy.
“With my bowling, I was a bit nervous after they’d made a good start. But, thankfully, it came off for me. I’m delighted.
“The ball seemed to follow me in the field. It was just one of those days.
“We’ve been pretty confident throughout the summer. Every 50-over game, we’ve felt like we’ve been it even when we’ve lost.
“Our warm-up games against the Lightning this week gave us confidence. This is a great win, and hopefully we can carry it on now.”
Thunder’s innings began poorly when Georgie Boyce departed for nought in the second over but Lamb and Ellie Threlkeld put on 33 for the second wicket before Threlkeld, having made 13, skied Gunn to backward point.
Rebecca Duckworth was bowled for a single by Linsey Smith but Thunder then enjoyed their best spell of the innings as Lamb and Natalie Brown put on 63 in 8.3 overs.
The dismissal of the pair in successive overs seemed crucial. Having reached her fifth T20 half-century off 38 balls, Lamb reverse-swept Katie Levick to Sterre Kalis at short third and Brown then pulled Phoebe Graham to deep square leg. Her departure for 31 brought ended the fluent scoring as only 18 runs came from the last five overs.
Langston bowled Laura Marshall to give her 2-32 and both Graham and Levick took 1-18.
But a fine end to the first half was marred when Sarah Taylor was struck in the face by Langston’s final ball, which lifted nastily. The former England wicketkeeper was escorted from the field and had to be replaced by concussion substitute Rachel Hopkins. Importantly, Taylor was unable to bat.
Thunder’s modest total seemed even smaller as Diamonds openers Hollie Armitage and Leah Dobson put on 31 in four overs but thoughts of an comfortable win were ended by Lamb, who trapped both Armitage and Ami Campbell leg before wicket in the same over.
From the Kirkstall Lane End, Sophie Turner was bowling brilliantly, conceding just four runs in her four overs and having Leah Dobson caught at cover by Lamb for eight.
Gunn and Kalis accelerated but their efforts faltered when Gunn was bowled by Jones in the 14th over, at the end of which 55 runs were needed.
Kalis was stumped by Threlkeld off Brown for a fine 32 and Diamonds lost further wickets in a desperate attempt to score 27 off the final two overs.
Diamonds spinner Levick said: “We were happy with how everything went in the first half, but second half we just got stuck. The top order have held their hands up.
“It’s a game we should have won, so hopefully there’s a bit of fire in the belly for the next game.
“Emma (Lamb) is a class player, and we know how confident she is at the moment after her 130 in the warm-up game against the Lightning this week.
“We were quite happy to keep her to just 50, but when she came on and took two wickets straightaway, that just changed the momentum and put us on the back foot.”