Englishman Rose's magical finish in regulation -- birdies at 14, 15, 16 and 17 -- allowed the 45-year-old veteran to pass 54-hole leader Tommy Fleetwood and world No.1 Scottie Scheffler and join J.J. Spaun, the reigning US Open champion, in the playoff.
"That was an amazing last 90 minutes," Rose said. "I never stopped believing. I played unbelievable golf coming down the stretch."
Famously beaten by Rory McIlroy in a playoff at the Masters in April, Rose shot three-under 67 to finish at 16-under 264 and Spaun had a 65 to join him in the playoff at TPC Southwind in Memphis on Sunday.
Scheffler (67) and Fleetwood (69) tied for third, one shot back.
Rose and Spaun both had birdie putts on the first playoff hole lip out, forcing a return trip to No.18. On their second tries, they converted birdie putts with Spaun's coming from 30 feet.
The hole location on 18 was changed for the third playoff hole and Rose dropped his birdie putt from 12 feet. Spaun's 7-foot attempt for birdie slid left of the cup.
Rose won for the 12th time on the PGA Tour and became the first winner on Tour age 40 or older this season. His last Tour win came at the 2023 AT&T Pebble Beach Pro-Am.
He jumped from 25th to fourth in the FedEx Cup points standings behind leader Scheffler.
The top 50 in the standings advance to the second round of the playoffs, the BMW Championship, which will be held at Caves Valley Golf Club at Owings Mills, Md., beginning Thursday.
"When I bring my best, I know I'm good enough to play and compete," Rose said. "And to now win against the best players in the world, it's a very gratifying day for me and a lot of hard work coming to fruition."
Jason Day was the lone Australian to advance to the BMW Championship, though he dropped from 37th to 44th in the standings after finishing tied 56th for the tournament at two over after a closing 72.
Countrymen Min Woo Lee and Cam Davis did not make the cut. Lee fell to 57th as he finished tied 68th at 10 over ..and Davis stayed 69th as he tied 50th at even par
Rose didn't play any practice rounds before the start of the St Jude and he skipped the Wednesday pro-am because of illness, but the absences didn't affect his play.
He had a chance to win on the 72nd hole, but his 13-foot birdie putt slid past the hole forcing the playoff with the 34-year-old Spaun. He had the exact same putt on the first playoff hole.
Spaun thought he had a solid opportunity to extend the playoff to a fourth hole with a 7-foot birdie attempt.
"It (stinks) to miss a 7-footer, but tricky read and I pulled it a little bit," Spaun said. "But yeah, I hung in there the best I could, and he beat me to the hole first. Just wasn't meant to be."
