The win was Purtzer's first on the Champions Tour after joining the circuit in 2001. He won five times on the PGA Tour, including the NEC World Series of Golf in 1991.
'It's so strange how things turn around,' said Purtzer, who earned $225,000 for the victory. 'It was kind of slipping away on the back side. This game is so strange.'
Morgan held a two-shot lead after Purtzer landed in a greenside bunker at the 17th and failed to get up and down for par. The two headed for the 546-yard 18th at Valencia Country Club, a familiar spot for both as the pair tied for third last season, narrowly missing out on the playoff between Tom Kite and Tom Watson.
On Sunday, Morgan hit a 3-wood off the tee, then badly pulled his second shot with a 3-wood, landing it several yards left of the green. Purtzer smoked his drive down the fairway and from 255 yards out, landed a fairway metal close to 60 feet short of the pin.
Morgan hit his third from the heavy rough 30 feet over the hole. Purtzer rolled home his long eagle try to reach 9-under par and tie Morgan, who had a difficult two-putt awaiting him.
Morgan's tricky downhill putt that could have won the tournament slid seven feet past the hole, meaning he had to drain that putt to force a playoff. Morgan missed the seven-footer and handed Purtzer the win.
'I've seen strange things happen before on this course, so I wasn't ready to quit,' said Purtzer. 'I wanted to make a three to get to 9-under, but I never expected to see Gil back up. He just doesn't do that.'
Morgan spoke of his play on 18.
'The trouble was on the right and I just pulled my 3-wood too far to the left,' he said. 'Then when I hit up there with a 9-iron, I left myself a tough 30-foot putt.'
Purtzer trailed Morgan by two after Friday's opening round and Saturday's second-round action was washed away by rain. Tournament officials shortened the event to 36 holes and Purtzer was quick to take advantage of better conditions on Sunday.
He parred the first three holes but went on a birdie run. Purtzer holed a 45-footer at the fourth and sank a 12-footer for birdie at the next hole. He made a pair of 10-footers for birdie at six and seven for four birdies in a row.
Purtzer went 1-over par in his next six holes to fall to 8-under for the tournament. He dropped another shot on 17 before the unlikely eagle at the last.
'I played the par-5s so poorly until 18,' said Purtzer. 'I was trying to make a three to get to 9-under but you don't think you will.'
Sammy Rachels and John Schroeder tied for third place at 6-under par, followed by Jim Thorpe, Des Smyth, Hubert Green and Allen Doyle, who shared fifth at minus-4.
Ray Floyd, who returned to action for the first time following successful prostate cancer surgery, shot a final-round 70 and tied for ninth place with Tom Wargo and John Bland at 3-under-par 141.