The Danehill filly was a warm order to follow up her easy victory in the Debutante Stakes at the County Kildare track four weeks ago, but the 2-7 favourite did not get things all her own way.
Fallon was forced to bring his mount wide down the centre of the track having dropped her out early.
And after a tooth-and-nail fight with 25-1 chance Ugo Fire, the pair lifted the 300,000 race by a neck, with 100-1 outsider Ardbrae Lady finishing third.
Although not setting the world alight, Rumplestiltskin was starting to gain the upper hand in the closing strides and was in command on the line.
"She pulls up when she get to the front. She's really only as good as the horses she's racing against she only just does enough," O'Brien said.
The Ballydoyle handler, winning the race for the fourth time in six years, indicated this may be Rumplestiltskin's last outing of the season before being put away for a Classic campaign. "She's a very smart filly and the 1000 Guineas next year would be a possibility."
Fallon felt the filly may have suffered some inference at the start, and he added: "She was bumped early on and I was lucky to finish."
O'Brien's charge had been a leading fancy for next year's Guineas but Ladbrokes were unimpressed with her performance and pushed her out to 16-1 from 10s.
Coral took less drastic action and left her unchanged at 12-1 for the Newmarket Classic, while William Hill cut her to 9-1 from 10s.
Mick Channon's Flashy Wings, who was taken out of the Moyglare at the final declaration stage on Friday, still heads the market with Coral quoting her at 7-1 while Ladbrokes and Hills go 8s.
Abigail Pett put herself in line for a crack at the Sky Bet Cheveley Park Stakes on September 29 when coming with a late run to land the Group Three Go And Go Round Tower Stakes.
Darren Williams had Karl Burke's British raider Clare Hills handily placed from the off and she was soon joined at the head of affairs by the 4-6 favourite Aussie Rules.
The pair enjoyed a battle for the lead for much of the six-furlong contest before O'Brien's charge last seen when finishing fourth in the Vintage Stakes at Goodwood started to pull clear in the final half a furlong.
However, Abigail Pett came from off the pace to pip Aussie Rules by a short head, with Golden Arrow taking third and Clare Hills finishing fifth.
Winning trainer Jim Bolger said: "She was in the Moyglare but we took her out at the forfeit stage as she had an injury.
"She looked around a bit on her first run so we decided to put the blinkers on here.
"Hopefully we will step her up now and we will have a look at the Cheveley Park Stakes."
Newmarket-based Mark Wallace tasted success at the Curragh for the second time this summer as Benbaun raced to success over the minimum distance in the Nolan & Brophy Auctioneers Flying Five.
Wallace's four-year-old took a Listed race at track in June and followed up with his first success at Group Three level.
Jamie Spencer sent the 9-4 second-favourite to the front entering the final furlong and the pair ran on too strongly for The Tatling, the 13-8 favourite, to take the race by a length.
Benbaun was having his first run since finishing fifth in the Nunthorpe, and Wallace said: "He sweated up badly at York but was nice and settled today.
"The horse likes it here and he is a pleasure to train.
"I have to give full credit to Jamie who is chasing the jockeys' title but still took a day off to come here and ride for me.
"I will have at look at the Prix de l'Abbaye for him but he needs fast ground and will probably be put out to grass now for three weeks. His main target is Hong Kong Sprint in December."
Chelsea Rose continued her resurgence with a smooth success in the Listed Dance Design Stakes.
Con Collins' three-year-old had bounced back to form at Leopardstown last month when seeing off Irish Field St Leger hopefuls Shalapour and Vinnie Roe in the Ballyroan Stakes.
Sent off the 2-1 favourite on the back of that effort, last year's Group One Moyglare Stud Stakes winner swept into the lead at the furlong pole to beat Pictavia by two lengths.
James Given's Summitville led for most of the way under Jamie Spencer but weakened close home and finished fourth.
"She is getting better all the time and we are very pleased with that she did it easily," said Collins' daughter Tracey. "There was a good pace on early and that suited us.
"All being well, she will be back here for the Blandford Stakes (September 18).
"She will then probably go for a fillies' Group One in Rome on October 23 (the Premio Lydia Tesio) and will probably be kept in training next year."
Kestrel Cross was produced with his customary late rattle to claim the ladbrokes.ie European Breeders Fund Irish Cambridgeshire, beating Jalmira by a length.