Chapple's declaration, after he weighed in with an unbeaten 34 off 29 balls, left the home side with a target of 287 to win off a minimum of 39 overs.
Farmer capped the win off with a memorable game-winning goal with 3 34 remaining in the contest.
If ever there was a match won off the bench, this was it – and therein lies the challenge.
In 2007, he won off a handicap mark of 161; in 2009, he won off 174; and last year, he ran his heart out in third off 182.
"To pull off a win out of this match is great.
Wales bade farewell to 100-cap Martyn Williams by killing off Shane Williams' hopes of a winning send-off for the Barbarians at the Millennium Stadium.
But Philadelphia may be motivated by a) having the chance to eliminate a division rival and b) giving Coach Andy Reid a winning send-off.
Barcelona gave Enrique a winning send-off as they beat Alaves 3-1 to win the Copa del Rey on Saturday.
The Irish will hope to give former skipper Trent Johnston, who will retire after the five-day game in Dubai, a winning send-off.
In a parimutuel market, a winning bet pays off a proportional share of the total stake on all outcomes.
