He still walked away $1.2 million richer.
Furyk became the fifth player, and second born outside South Africa, to successfully defend his title at the Nedbank Challenge despite shooting a 2-over 74 on Sunday -- his worst round by six shots.
The world's second-ranked player started the day with a three-shot lead over Padraig Harrington and ended it with a two-shot win over Henrik Stenson. He finished at 12-under-par 276.
Stenson, the first-round leader, was the only player to break 70 on Sunday, shooting a three-under 69 to end at 10-under 278. Harrington had a 3-over 75 and finished fourth at 8-under 280.
Ernie Els, a three-time champion, shot a 72 and was fourth at 7-under 281. Charl Schwartzel, the only player not ranked in the top 20, also had a 72 and was a shot further back at 282.
Furyk played flawlessly through the first three rounds, allowing for some missteps Sunday.
His first bogey of the tournament came at his 57th hole, the par-4 third. He later bogeyed the par-4 eighth to drop to 14 under, but Harrington made a double-bogey there to fall six shots off the pace at 8 under.
Furyk made his third, and last, birdie at No. 9 before carding back-to-back bogeys at 11 and 12 -- both times from a bunker. He was at 13 under and still had a four-shot lead on Harrington.
Five stabilizing pars followed, and a closing bogey at the 18th only affected his margin of victory.
For Furyk, who led for three straight rounds, the victory was a lot simpler than last year's, when he needed a chip-in birdie to win a four-way playoff.
This year, his triumph was aided by the inconsistent play of some of the world's best golfers.
Retief Goosen shot a 3-over 75 on Sunday and finished 10 shots back in sixth place at two-under 286. It was his fourth consecutive round in the 70s.
Sergio Garcia (71) and Trevor Immelman (74) were a shot further back at 287, while Chris DiMarco ended on even-par 288 following a 73.
David Howell opened with a 69 on Thursday, then progressively got worse. He had a 76 in the final round and was 10th at 3-over 291. Jose Maria Olazabal posted the highest score Sunday with a 79 and ended 11th at 4-over 292.
Colin Montgomerie was last after each round. He closed with a 76 on Sunday and finished 22 shots off the pace at 10-over 298.