Danielle Frasier of Encinitas, Calif., won the girls division by seven strokes.
The 15-year-old Paolucci closed with a 1-over 73 to match Spieth (68) at 12-under 276. Paolucci made a double bogey on No. 17, then made a 2-foot birdie putt on No. 18 to force the third playoff in tournament history.
I stopped that 64-degree wedge on the last hole a dime pretty much. Thank goodness I had that club in my bag, Paolucci said. Then after Jordan and I both missed putts on the first playoff hole, I made a putt on the second to win.
Both players made par on No. 18, the first playoff hole. They then moved to No. 7, a par-3. Both players hit the green, but only Paolucci was able to convert his putt.
I was so happy to make that 6-footer, Paolucci said. I struggled coming down the back nine, but pulled it out in the end when it mattered.
I thought after the first few holes it was going to be a great round, but then a few missed putts and it was tough. It was a battle out there today. Im so happy to win, but wish I could have played a little better.
Spieth overcame a five-hole deficit in the final round.
All I wanted to do coming here was make the Junior Ryder Cup, and I did that, Spieth said. I played a consistent round with no bogeys and that is definitely what I wanted to do. I would have liked for a couple of more putts to drop and I left a couple short, too.
Jeffrey Kang of Fullerton, Calif., and Luke Guthrie of Quincy, Ill., tied for third, a stroke back. Kang shot a 68, and Guthrie had a 74.
The 15-year-old Frasier finished with a 68 for an 11-under 277 total.
This is the biggest tournament that I have ever won, Frasier said. It is especially good because I was in the lead all four days. I am usually coming from behind when I win so it is nice to win when I have been in front of everyone else.
She made five birdies on the back nine.
I was telling myself to be patient all day and the putts finally started dropping and I extended the lead, said Frasier. I came here to get into the Junior Ryder Cup. Winning the Junior PGA Championship was a huge bonus.
Sarah Brown of Phillipsburg, N.J., finished second. She closed with a 70. Alexis Thompson of Coral Springs, Fla., the 2007 winner, was another stroke back after a 70.
The final two spots on the Junior Ryder Cup team were granted to the winner and runner-up in both divisions. The matches against Europe are set for Sept. 15-16 at The Club at Olde Stone in Bowling Green, Ky.
Anytime you get to represent your country and play in the Junior Ryder Cup it is an honor, Paolucci said I am excited to play on the American team this year.
PGA of America past president Ken Lindsay added two captains picks Saturday, Kang to the boys side and Tiffany Lua of Rowland Heights, Calif., to the girls team.
Leading the boys side will be Cameron Peck of Olympia, Wash., the No. 1 ranked junior player and U.S. Junior Amateur winner.
Joining Peck will be Cory Whitsett of Houston, and Andrew Yun of Chandler, Ariz.
Thompson also is on the girls team along with Jennifer Johnson of La Quinta, Calif., and Erynne Lee of Silverdale, Wash.