Switching from a Nike Method Origin putter to a Scotty Cameron Concept M1 Prototype brought about a change of fortunes for McIlroy as he won his first PGA Tour title in 16 months at the Deutsche Bank Championship three weeks ago.
McIlroy, 27, vaulted into the playoff with a barnstorming finish to his final round, holing out from 140 yards (128 meters) to eagle the same hole where he would clinch the win 90 minutes later.
"To play the way I have in the last few weeks to get it done is very special", the World No.3 added.
The real heartache belonged to Chappell, who played superbly for so long until one tee shot on the 17th tumbled into the nasty rough and led to bogey. McIlroy started two-shots back on -6.
"It was nice just to roll one in on top of him and get this thing done".
McIlroy looked shellshocked but regrouped to sink a seven-footer and stave off defeat at the third extra hole, before clinching it at the next.
2 - Ryan Moore produced a superb final round and playoff display but came up just shy of an inspired McIlroy.
"It didn't feel right because I didn't win the Tour Championship", Johnson said.
"When you have a six-footer to win the Tour Championship, the FedEx Cup, $11.5m, and you feel like you did a good putt and it doesn't quite go in - I just had to regroup, stay focused, and try to give myself chances in the play-off, and thankfully I stayed patient enough to get it done".
"I couldn't control what anyone else did", McIlroy said.
"There's a lot of things that had to go well for me today, along with me playing well", the four-time major victor said after the round.
Day won three times this year as well, taking the Arnold Palmer Invitational, World Golf Championships Match Play and The Players Championship.
It took three more holes for the Tour Championship to be decided and McIlroy eventually sealed it with a superb birdie at the 16th. He had a 20-foot birdie chance on the last hole that he left woefully short, and he failed to birdie the 18th again in the playoff.
Nothing was bigger than that birdie at the end. He led the standings going into the Tour Championship after his victory in the BMW, and he took the lead into day four at East Lake.
Moore had to wait to see if his performance - a 66-64 weekend at East Lake - was worthy of a captain's pick.
It is the first time McIlroy has won the season-ending playoffs.
North, who won the U.S. Open in 1978 and 1985, is extremely confident that Davis Love III's American team can prevent Darren Clarke's Europeans from bagging the trophy for an unprecedented fourth straight edition. In those final rounds, Chappell's scores were 67, 69, 69 and 66.