It could be a bumper day for the McIlroy family if Rory manages to win golf's oldest major at Royal Liverpool.
McIlroy is currently six shots ahead of nearest rival Rickie Fowler going into the final round of the tournament - although with 18 holes to play it is far from a foregone conclusion that he will take the title.
Not only will Rory win almost £1 million in prize money, but dad Gerry and three friends will be in line for a £200,000 payout after making a cunning bet some ten years ago.
The quartet put £100 each at odds of 500/1 on Rory to win the Open before his 26th birthday.
Gerry is not the first sporting parent to cash in on a child's sporting success.
Goalkeeper Chris Kirkland's dad Eddie won £10,000 after wagering £100 that his then teenage son would turn out for England before the age of 30 - a prediction that came true when Chris came on in a friendly against Greece in 2006.
That looks like a relatively piffling sum, however, when compared to the grandfather of teenage footballer Harry Wilson.
Peter Edwards netted a cool £125,000 after sticking £50 on Harry to play for Wales when the boy was just 18 months old.
Apparently Peter had noticed his grandson's fondness for kicking a ball around and went to a local bookies in Wrexham to make the unusual bet.