Mickelson said he felt close to shooting a good score and that his seven-birdie round could be a launching pad for next week's second event in the FedExCup playoffs, the Deutsche Bank Championship in Boston.
"Yesterday after the round, I felt a good round coming, because the pieces were there for a low round yesterday but I didn't put it together," said British Open champion Mickelson, referring to his third-round 70 on Saturday.
"I made a lot of little mistakes. I just played sloppy but I felt my ball-striking was coming and I felt the putter was coming.
"I feel like now, my ball striking is coming around. It was pretty sharp. I feel really good on the greens and I'm looking forward to getting to Boston next week."
Mickelson began the day tied for 34th at three under par after rounds of 71-69-70 and finished tied for sixth, at one stage standing within a stroke of the lead before slipping with a bogey at the 18th.
The big left-hander said the pressure was off on Sunday since he began the final round nine shots off the pace and he had no specific target.
"Being nine shots back starting the day, you don't think you had a chance," he said.
"It was just to play a good, solid round, to play smart, to hit the shots and to miss it in the proper spots and play a good, solid round and use it as a motivation or momentum-builder for next week."
His stretch of seven birdies in 10 holes from the sixth, however, was nearly good enough to help catapult him to the top of the leaderboard.
"I do believe, had I made one or two coming in, I might have had a chance," he said.
Mickelson, who is a member of Liberty National, feels at home on the waterside layout perched on the edge of New York harbor and called it an enjoyable week in front of area fans who have long embraced him.
"I love playing here. I love playing in the metropolitan area - New York, New Jersey. It's just terrific," said Mickelson, who even enjoys the running banter from vociferous fans.
"The people are really fun to play in front of. They are just fun," he said.
"It's probably my favorite place to play. They have been great to me and my family, and I love some of the comments. It's funny."