The Italian jockey made his move wide of the far side group and only got up in the closing stages on the 14-1 shot.
Dettori had to be at his strongest to win the £150,000 sprint handicap by a head from Barney McGrew (20-1) Knot In Wood (11-1) was three-quarters of a length away third with Evens And Odds, the 7-1 favourite, fourth.
The race was the main event of
the three-day meeting at the Ayrshire course which started on a poignant note with a piper playing a lament and a silence being observed in memory of tragic apprentices Jan Wilson and Jamie Kyne.
It was also announced that this year's apprentice jockeys' championship has been renamed in memory of the two young riders who died in a fire in Malton this month.
The title race will now be known as the Jan Wilson and Jamie Kyne Apprentice Championship 2009 after families of both promising apprentices gave their blessing to the tribute.
Kevin Darley, chief executive of the Professional Jockeys' Association, said: "This is an excellent gesture by the sponsor. It is most appropriate that this season's apprentice championship is renamed in memory of Jan and Jamie."
The main event on Thursday was the Kilkerran Cup and the class 2 race went the way of the Noel Wilson trained Demolition.
The 9/1 chance ridden by Gary Bartley claiming 5lb always travelled well just behind long time leader Bucked Off and when the chance came in the closing stages, Bartley made for home and his mount responded well to the call holding off a late challenge by Plaisterer ridden by Jack Mitchell.
After the win, the victorious Wilson said: "The handicapper has had him all year. He won a mixed-up race at Beverley where they went very fast up front and they put him up 8lb, but he has gradually let him off.
"Gary has now ridden six winners from 12 rides for me. I said to him that he gets a mile four so not to let them queue up in behind, I said to go forward and kick on. This lad is well worth his claim. There are a lot of good 5lb claimers around but he is one of the
best.
It was also a great start to the festival for the on-form duo of Richard Fahey and Paul Hanagan who notched up a treble each
Friday saw the inaugural running of the William Hill Ayr Bronze Cup and this race was always going to give an indication of where the winner of the Silver and Gold Cups could come from.
As expected, the runners in the Bronze Cup split into two groups and it was the low numbers that had the advantage.
Brunwynd Boy drawn in stall one led from the off and was still challenging at the run-in, However, 5lb claimer Barry McHugh riding 16-1 shot Baldemar, managed to overhaul the long-time leader close home to win the contest.
Ingleby Lady, drawn in stall two, snatched second in the dying strides, whilst Brunwynd Boy had to settle for third and Jim Goldie's Esoterica completed the clean sweep for single figure stalls in fourth.
The winning jockey said: "It turned out perfect for me, they went pretty quick in front and I just sat and waited. He was always going to grind it out."
Baldemar's trainer, Richard Fahey was in high spirits following his victory, he said: "To be fair this is Karl Burke's horse really and I was just lucky to get him.
"I always felt they were going quicker on the far side and I did take out of the race that I don't think the draw is such a big bogey - I wouldn't like to put my last 10p on saying the far side will win the Ayr Gold Cup but we will see
"Three runners without a winner - I was getting a bit depressed! And this is my race, nobody else has ever won it! Fair play to William Hill - it is a £30,000 sprint handicap, which is great - take your hat off, we are always quick enough to knock the bookies but this is a fantastic idea.""
Elsewhere on Friday's card there was the Harry Rosebery Listed Stakes Race and it was the turn of the sprint king Dandy Nicholls to get in on the action with Mister Manannan claiming a 3½ length victory ridden by his son Adrian.
After the win Alex Greaves, Nicholls' wife, said: "He is a really nice horse and he deserved this - he is always honest and he deserved to win one of these.
"We knew there would be plenty of pace on and we knew that Skylla would go on, but he had the ability to sit on his tail and the ability to go on when asked.
"He ran really well at Doncaster and, to be honest, we would have been disappointed if he had got beaten.
"I don't know if he will run again this year and I will have to speak to the owner, but he owes us nothing for the year."
As the action got under way on Saturday, the first of the main races was the Ayr Silver Cup and it was that duo of Fahey/McHugh who struck again with Kaldoun Kingdom pouncing in the closing stages to take the race and completing a historic double in the process.
Lowther finished second and Green Manalishi took third place. Mastership stayed on to take fourth.
The victorious Fahey remarked afterwards, "I thought the ground would be quick enough for him but they said on Thursday that Baldemar wanted softer ground - it is beautiful ground with plenty of juice in it.
"These were his ideal conditions and he deserved this - he will probably go for the Coral Sprint at York now."
The next race on the card was the Laundry Cottage Stud Group 3 Firth of Clyde Stakes and 33/1 shot Distinctive stole the show with an easy victory for trainer Bryan Smart.
Coming from stall 3, the winner, ridden by Tom Eaves, moved along quite nicely and when Eaves asked for more the winner quickened up and won the contest with ease.
Bryan Smart commented: "That wasn't a surprise after the way she worked at Redcar the other day. I have never seen a jockey with as big a smile as Tom had that day - you couldn't have knocked it off with a stick. We came here with a good chance.
"She has been slow to come to hand and we have taken our time with her but I have always liked her. It is nice to have a decent filly again and she is something to look forward to for next year.
Smart added: "I will talk to Gary and Lesley before we make a decision on whether she will run again this year but next year we will probably have to run her in a Guineas trial - she is bred to get further."
After the excitement of the Gold Cup the next race was the 1mile 2f Doonside Cup and the powerful Godolphin team were double handed for the event with Prince Siegfried and Baila Me.
Godolphin horses are in top form at the moment and it was no surprise to see a one-two from the stable.
Frankie Dettori, fresh from winning the Gold Cup on Jimmy Styles, was in no mood to lose the winning streak.
The Italian maestro took the race by the scruff of the neck early on and was leading as the runners came on to the home straight. The quick-thinking Dettori then steered his mount into the middle of the track and used the fresher ground to bring home the winner in impressive style.
In second place was Baila Me ridden by Alan Munro and in third place was Arch Rebel for Irish trainer Noel Meade who is normally associated with National Hunt racing and was ridden by Ballydoyle jockey, Colm O'Donoghue.
Another great Ayr Gold Cup Festival has been and gone. I spoke to racecourse head of PR Iain Ferguson on Monday he was delighted to tell me that crowd numbers were actually up on last year despite the economic downturn
This is great news for the racecourse and the local area in general. The Ayr Gold Cup still attracts race-goers from around the country and this year
they were not to be disappointed with either the quality of the fields, record numbers of entries or the condition of the track.
On the racing front, we almost had a historic treble with Richard Fahey and Barry McHugh winning the Bronze and Silver cups and coming third in the Gold Cup but if you ever wanted a gatecrasher it would have to be Frankie Dettori.
Dettori arrived in style, won in style and celebrated in style and added the finishing touch to the William Hill (Ayr) Gold Cup Festival 2009.