Laurens put the seal on a tremendous season for trainer Karl Burke with a thrilling victory in the bet365 Fillies' Mile at Newmarket.
Having won the May Hill Stakes at Doncaster last month, the 10-1 chance was stepping up to the highest level for the first time and raced on the speed throughout.
With the rail to help, PJ McDonald kicked for home inside the final two furlongs and after shaking off stablemate Ellthea and Magic Lily, looked set to win decisively.
However, September was travelling strongly in behind and once the gap came she fairly flew home to virtually join Laurens on the line.
After a nervous wait, the judge confirmed Laurens had held on by a nose, denying September's trainer Aidan O'Brien his 24th Group One success of the season.
Magic Lily was not far away in third, with O'Brien-trained 15-8 favourite Magical fourth.
McDonald, who rode the winner of the Scottish Grand National during his days as a National Hunt jockey, was claiming his first ever Group One success on the Flat.
He told ITV Racing: "I honestly can't believe it. I'm 35 years of age now and the relief when that number got called out was amazing. If I never do anything else in my career, I've ridden a Group One winner.
"I didn't have a clue whether we'd won. I was praying we had it, but I didn't know.
"All the credit goes to Lucy (Burke, trainer's daughter). She rides this filly every day and has done since she came in.
"It's a massive team effort, everyone has played their part. It's brilliant."
North Yorkshire-based Burke, who has also enjoyed Group One success with the colt Unfortunately during this campaign, as well as a host of other notable successes, said: "That was good, apart from the last two strides!
"I was praying her number would be called. I popped into the bookies and watched the replays and a few lads in there said she held on and they are usually right.
"She's a very high-class filly and we always knew that. She is a galloper rather than a speed horse at this stage of her career.
"When we step up to a mile and a quarter or even further next year, she's going to be very good.
"I would rather her take a lead as she's such a green filly, but we had to let her use her stride.
"She was a beautiful, classy-looking yearling. She wasn't a cheap horse (£220,000), but she has this fantastic action - she's like a ballerina and very light on her feet for a big filly. We've never had her off the bridle at home."
He added: "PJ has got a great work ethic. He works really hard and rides out whenever you want him. I think the Mark Johnston connection has really helped him and given him that confidence. Luckily we've had a few nice horses for him to ride this year."
Laurens was given a 14-1 from 25-1 quote with RaceBets for the Qipco 1000 Guineas, with Paddy Power going 8-1 from 20-1 for the Investec Oaks.
Burke said: "That is a distinct possibility (Guineas). We've got a lot to talk about. I suppose if the Guineas came up on soft ground that would be a big option, but we will sleep on it and go through all the options.
"I think the ideal race for her next year would be the Prix de Diane (French Oaks) over a mile and a quarter, but we'll sit and think. We've got plenty of time."
Winning owner John Dance said: "It's unbelievable. As the day has gone on I've just felt more and more grateful that we've got a filly that even got us here.
"I got a bit more relaxed as we got closer to the race, just feeling it was an honour to be here.
"To have won it is insane. It's absolutely crazy for owners like us, taking on the big boys. Hopefully we've got a champion two-year-old filly."