McIlroy signed off with a level par 70, seven shots back of winner American Jason Dufner.
"I saw a lot of great signs out there today," said McIlroy.
"Hopefully I can just bring that through to the next few weeks and have a strong finish to the season."
Struggling through a season that has had more downs than ups after switching his club brand to Nike in a lucrative deal reported to be worth $250 million (£160 million), McIlroy displayed plenty of fighting spirit during a rollercoaster week.
McIlroy, who coasted to victory by a record eight strokes in last year's PGA Championship at Kiawah Island, had not given up on his title bid this week, even after flirting with the cutline during the second round.
After playing his way back into title hunt with a 67 on Saturday, McIlroy effectively sank his title defence when he hit his second shot at the par-four fifth into water en route to a triple-bogey before hitting back with three birdies to finish on three under for the tournament.
"I actually didn't hit a bad shot, pitched it just in the place where you can't pitch it I guess," said McIlroy.
"If I had of been a few feet right or a few feet left, it would have been fine, but just pitched in that difficult depression and came back into the water.
"I really didn't hit a bad shot, but obviously it was disappointing. Came back okay at the end."
The 24-year-old, who has been desperately searching for form is convinced he saw evidence that he was close to getting back to his best.
"I played the best golf of the week today. I hit some really good drives and really good iron shots," enthused McIlroy.
"Didn't quite putt as well as I did the first three days, but really, really happy with my game going into the next few weeks.
"I didn't hit many bad shots out there today."