As captains of the Rest of the World and the Great Britain & Ireland teams respectively, both dearly want to lift the trophy at the end of the six-race competition.
But they are also involved in a terrific tussle for the Flat jockeys' championship.
And there is the added bonus of a silver saddle prize for the leading jockey at his afternoon's meeting.
The sponsors made Dettori 11-4 market leader after he picked up five mounts with solid-looking chances at Thursday's draw.
The top two in the title race clash in the opening Prince's Trust Shergar Cup Distaff, with Dettori on Fruit Of Glory for John Jenkins and Fallon aboard Proud Boast for David Nicholls.
Fallon sits out race two, the Shergar Cup Juvenile, but Dettori is in action on the Ian Wood-trained Justaquestion.
In the Murphy's Fastflow Shergar Cup Mile, Fallon teams up with the Andrew Balding-trained Pentecost, last year's winner and the likely favourite, with Dettori on Bob Jones's Unshakable.
Dettori misses out in race four, the Sodexho Shergar Cup Stayers' Handicap, with Fallon on Penny Pictures for champion jumps trainer Martin Pipe.
The Italian has the plum ride on the strongly-fancied Starry Lodge for his former boss Luca Cumani in the Carvill Shergar Cup Challenge Handicap, while Fallon will be on Hambleden for Michael Jarvis.
In the concluding Dubai Duty Free Shergar Cup Sprint Handicap, Fallon has drawn top-weight Glaramara, trained by Alan Bailey. At the other end of the handicap, Dettori partners Doitnow for Richard Fahey.
Former champion jockey Michael Roberts, the Dubai Duty Free Rest of the World team selector, said: "I believe we can retain the Shergar Cup. We have got some nice horses and two very strong favourites in Starry Lodge and Double Obsession.
"I did not expect to get both and it is a huge advantage to have Frankie on Starry Lodge. Double Obsession seems well in he ran so well in the Goodwood Cup at Goodwood and Mark Johnston's horses do very well at Ascot.
"Frankie has one or two decent rides and he should do well."
The Rest of the World team is made up of Dettori, Weichong Marwing (South Africa), Damien Oliver (Australia), Yutake Take (Japan), Gerald Mosse (France) and Dario Vargiu (Italy).
Backing up Fallon in the Sodexho Great Britain & Ireland team are Johny Murtagh, Darryll Holland, Kevin Darley, Michael Kinane and Jamie Spencer.