Jordan Clark fired Lancashire into NatWest T20 Blast finals day with four wickets in eight balls without conceding a run as the Lightning came from a long way behind to beat Glamorgan by one run in a thrilling quarter-final at Emirates Old Trafford.
Thanks in large part to Clark, Lancashire were able to defend a modest total of 137 for eight - built around Usman Khawaja's 67 off 54 balls - to progress through to their fifth appearance in last act of the competition.
All-rounder Clark, 23, was introduced into the attack for the 14th over of the Glamorgan chase, with the visitors seemingly cruising at 88 for two and Jacques Rudolph unbeaten on 33.
But Clark's right-arm pace accounted for the wickets of Murray Goodwin, Chris Cooke, Stewart Walters and David Lloyd as the Welsh county slipped to 100 for six after 16 overs, still needing 38.
The latter three dismissals were part of a triple-wicket maiden for the bowler, who had only taken four wickets in 10 previous Twenty20 spells throughout his four-season career.
Immediately after that over, the players came off for rain for the second time in a match which was washed out on Friday night and then had the start delayed by 75 minutes on Saturday.
When play resumed, Glamorgan lost Graham Wagg to Kyle Jarvis in the 19th over before Clark was left to successfully defend 15 off the final over and six off the last ball against Andrew Salter.
Clark finished with 4-22 and Rudolph 67 not out off 49 balls.
Glamorgan were in charge for the majority of the contest. Seamers Wagg and Michael Hogan struck three times each in restricting a depleted Lancashire side, having elected to bowl.
Off-spinner Salter snared two scalps as Australia batsman Khawaja hit a career-best 67 with six fours and a maximum.
Lancashire, without Junaid Khan, Jos Buttler, Kabir Ali and Andrew Flintoff to international duty or injury, never really got going in their innings, aside from a third-wicket stand of 40 in 29 balls between Khawaja and Karl Brown to advance the score from 19 for two early in the fourth over.
They lost wickets regularly from the eighth over onwards and stumbled as the Glamorgan attack expertly took the pace off the ball.
Australian Hogan struck three times at the death, in the 18th and 20th overs, including the key wicket of compatriot Khawaja.
Glamorgan looked on track to chase that total down as captain Jim Allenby, Goodwin and Rudolph helped them recover from the early loss of Mark Wallace with the total on five.
Rudolph was forced to come in at number three in the order instead of opening having jarred his left shoulder while trying to field a ball at long-leg late in Lancashire's innings.
But, while he seemed to have recovered after an hour's rain break, his contribution was not enough.
Lancashire's match-winner Clark was jubilant after playing a big part in his side's victory.
"A win in the quarter-final getting us through to finals day, I couldn't ask for anything more really," he said.
"It was just kind of going back to basics and trying to hit the top of off stump. Restricting them to five an over wasn't going to win us the game. We needed wickets.
"Sometimes it's your day, and it was mine with the ball. When the opportunity comes, you've just got to take it."
Glamorgan captain Allenby was pleased the game was able to take place but was left to rue the defeat.
"Firstly, full credit to Lancashire and the groundstaff. They did an amazing job with the rain that's fallen to get us out there," he said.
"To lose by one run is a shame, especially when we were going so well there at one point.
"Lancashire are a good side who never give up and came through with the win. We're disappointed because we could have won that game, but sometimes you've got to credit the opposition."
Meanwhile, Goodwin's appearance made him the oldest player to play in the knockout stages of domestic English Twenty20 competitions at 41 years and 234 days old.