SILVIS, 12 Jul 2015 (AFP) - Coming off his second John Deere title in three years will give Spieth an extra spring in his step as the world number two tries to continue his run at history at St. Andrews.
The 21-year-old American made par on the par-four second playoff hole while Gillis missed the fairway with his tee shot and then found the water on his second at the TPC Deere Run.
Spieth closed with a three-under par 68 to equal Gillis at 20-under-par 264. Gillis, who was three groups ahead of Spieth, fired a 64.
Once again, Spieth showed his flair for the dramatic as he rallied from eight shots off the lead after round one to earn his fourth US PGA victory of the season and the fifth of his career.
Spieth rallied from six shots back here in 2013 for his first career win, becoming the first teen to win on the US tour in 83 years.
Spieth was criticized for playing the John Deere instead of heading to Europe to prepare for the Open, but it appears he made the right move as he aims to collect the third leg of the calendar Grand Slam.
Gillis, 46, will have to console himself by claiming a spot in the British Open for the third time, having also competed in 1999 and 2008.
Former winner Zach Johnson fired a 65 and was joined in third place on 265 by last week's Greenbrier Classic champion Danny Lee (67) of New Zealand.
Americans Johnson Wagner (67), Chris Stroud (63) and Justin Thomas (67) shared fifth at 266.
Defending champion Brian Harman closed with a 67 to finish in a tie for 24th, nine adrift of the leaders.
Leading scores after Sunday's final round of the US PGA Tour John Deere Classic (x-won in a playoff, USA unless noted, par-71):
264 - Tom Gillis 66-65-69-64, x-Jordan Spieth 71-64-61-68
265 - Zach Johnson 66-68-66-65, Danny Lee (NZL) 68-68-62-67
266 - Johnson Wagner 68-63-68-67, Chris Stroud 68-68-67-63, Justin Thomas 63-67-69-67
268 - Steve Wheatcroft 67-66-70-65, Daniel Summerhays 65-67-68-68, Kevin Chappell 68-69-64-67, Will Wilcox 66-66-69-67
269 - Jason Bohn 68-68-69-64, Carl Pettersson (SWE) 66-71-66-66
270 - Scott Piercy 67-69-67-67, Robert Streb 66-70-68-66, Luke Guthrie 64-70-67-69
271 - Jerry Kelly 70-66-67-68
272 - Vijay Singh (FIJ) 67-68-70-67, Kyle Stanley 67-71-67-67, Brian Stuard 66-68-68-70, Adam Hadwin (CAN) 68-70-69-65, Roger Sloan (CAN) 70-68-67-67, Scott Pinckney 66-66-71-69