Allenby is this year's top Twenty20 run scorer with 354 in seven innings
Leicestershire's James Allenby was the destroyer at Liverpool as Lancashire missed the chance to nail down a place in the last eight of the Twenty20 Cup.
Allenby hit 69 in 45 balls as the Foxes closed on 146-5, before Kiwi paceman Iain O'Brien then took 5-23 as the home side were bowled out for 138.
Victory for Lancashire would have enabled them to become the first team to reach this year's quarter-finals.
But Allenby's third fifty in seven knocks set up the Foxes' eight-run win.
The English-qualified Western Australian was already the top run scorer in this year's competition before Monday night's latest effort at Aigburth.
He has now moved that total on to 354 in seven knocks. But he needed a lucky break to get going, top-edging Andrew Flintoff's second ball over the head of wicketkeeper Gareth Cross for four.
But he was then largely responsible for Lancashire shipping 53 runs in their next four overs as Allenby opened up.
Flintoff, like Mahmood, went for 17 in one over. And Aussie Allenby won his duel with the England all-rounder by putting him over the long-on rope for a steepling straight six.
Flintoff bowled his four overs for 29 but 23 off those came off the first two and he did at least come back well.
Once Allenby had gone, bottom edging into keeper into Cross's gloves as he tried to sweep spinner Stephen Parry, Flintoff returned to bowl his last two for just six runs.
Lancashire had won their previous six Twenty20 ties before the 18-day mid-tournament break. But the addition of Flintoff and fellow Test star VVS Laxman did not provide its expected advantage.
After one over from left-armer Harry Gurney, the home side looked bang on course.
Gurney went for 14 after three balls were called wide and then Steven Croft carved him behind square for two boundaries.
But Gurney's replacement O'Brien proved a lot more successful.
After getting rid of opener Paul Horton, he then bagged Flintoff too, fifth ball, deflating the sell-out crowd in the process.
Surprising Flintoff with a short delivery, the England all-rounder could only balloon a simple catch to square leg to earn O'Brien the second and most important of his five victims.
Francois du Plessis then went in the same over and, in his next, he snared Croft too for 40, to a diving catch on the square leg boundary.
Lancashire never quite recovered from being reduced to 58-4. And, although Laxman (18) and Mark Chilton (34) briefly offered hope, the home side's challenge finally ended off the penultimate ball.
It was Leicestershire's fourth win in seven games to keep alive their hopes of qualifying for the last eight.
They now travel to Trent Bridge for the local derby with Nottinghamshire on Wednesday night (1730 BST), while Lancashire are next in action the following evening in a floodlit game at Derby (1910 BST).
Lancashire skipper Glen Chapple told BBC Radio Manchester:
"We thought we'd bowled really well in limiting them to the score they got. But we came unstuck.
"I thought their total was slightly under par, but these games are there to be lost as well as won.
"It would have been nice to qualify but it's now down to us to get our confidence back up for the last three games."
Leicestershire all-rounder James Allenby told BBC Radio Leicester:
"It all seems to be going pretty well at the moment. More often than not the ball's hitting the middle of the bat.
"Batting up top is working very nicely for me. It's the best place to bat.
"If you are in that position you have a lot of responsibility to get the team off to a good start and make big scores. I've managed to do that a few times this season and I'm really enjoying it. We're going really well."
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