Jacobs appeared to be in command with a beautiful chip that lead to a three-foot birdie at the par-5 14th. He reached 12-under-par with the birdie and had a two-shot advantage over Aoki and Watson, who were in the clubhouse at 10-under.
Jacobs missed a pair of 20-footers for birdie at Nos. 15 and 16 but ran into trouble at the par-3 17th. His tee shot went right, almost going right of the greenside bunker but he found the sand. He blasted out to six feet and missed the par save but he did drain his tricky three-footer to maintain the lead, which was trimmed to one shot.
At the par-5 18th, Jacobs' drive went left into a hazard, forcing him to take a penalty. He roped his 3-wood from 255 yards short of the green but recovered nicely with a pitch that left him in tap-in range for his par and the clubhouse lead at 11-under-par.
In the group behind Jacobs, Fleisher reached 9-under-par but capitalized at No. 17. His 5-iron rolled within three feet to set up birdie and give the reigning U.S. Senior Open champion a chance to sneak in and win the tournament at the closing hole.
Fleisher also found trouble off the tee at Crandon Park Golf Club but his was right and the ball landed deep in a group of trees. He could not even reach the green with his third shot but he knocked it very close from 97 yards for his fourth.
Fleisher needed to hole his wedge shot to make birdie and force a playoff and he threw his approach over the hole. The backspin brought the ball close to the cup, but not close enough, stopping a foot from the hole and giving Jacobs his fourth career Senior Tour victory and his first since 2000.
'I didn't know whether to hit an iron, a 3-wood or a driver, but I know all my friends that I play with back home, if I hit an iron, they'd be laughing their rear ends off,' said Jacobs, who pocketed $217,500 for the victory. 'I thought, 'Man I got to go with a driver.' And I choked like a dog.
'I hit probably the best 3-wood I ever hit in my life. When I dropped it, I didn't drop it in a very good lie and I thought I better go for the green.'
'John just bogeyed 17, he knocked it in the water on 18 and I kind of wished I hadn't heard that,' said Fleisher, the two-time champion of this event in 1999 and 2000. 'I had an opportunity. I was there. I put myself in position and I couldn't handle it.'
Jacobs was solid from the beginning of his final round. He birdied three in a row, starting at four and added an 18-foot birdie at No. 8. Jacobs parred the ninth but birdied the 10th and tapped in for birdie at No. 11 to reach 11-under-par.
Watson shared the lead, but dropped a shot at No. 15 to fall down by one. He missed makeable birdie putts the rest of the way in until a birdie at the closing 18th.
'I had a lot of opportunities,' said Watson, who holed a 7-iron for eagle at No. 5. 'When it gets down to the short putts, that's where I've been having problems. I let it slip away.'
Tom Kite shared fifth with overnight leader Jay Overton at 9-under-par. Kite posted a 68 Sunday while Overton, a Monday qualifier, shot a 70.
Tom Purtzer, playing in his first Senior Tour event, carded a 3-under 69 and finished tied for seventh with Walter Hall, Sammy Rachels, Ted Goin and Bob Gilder. The group finished at 8-under-par.
Fuzzy Zoeller, also in his first official event on the elder circuit, tied for 51st at 1-under par.
Due to heavy storms on Friday, the first round was canceled and the tournament was reduced to 36 holes.
Full-Field scores from the Royal Caribbean Classic