(CNN)When Henrik Stenson pointed out to Jordan Spieth that his tee was slightly ahead of the marker, the American thought he must've narrowly avoided disaster.
However, it made no difference as instead of teeing off from the ninth, three-time major winner Spieth and 2016 Open winner Stenson were teeing off from the 17th.
Playing in the opening group of the final round of the Hero World Challenge, the pair did not realize that tournament officials had swapped the ninth and 17th tee markers for the last round.
"We kept our heads down off the finishing out on hole No. 8," Stenson explained, "and walked to the ninth tee box that we did on Wednesday, Thursday, Friday, Saturday.
"Put the ball down and hit some beautiful tee shots. Then when we went down to the hole, went down to the balls."
According to the PGA Tour, someone working in the TV trucks picked up on the error and informed chief referee Stephen Cox about the infraction.
"The rules official said: 'Did you hit off the right tee box?'" Stenson said. "And we're like, well, yeah, kind of -- and then we looked back and saw that there was another one forward and left."
Having been notified of the mistake, the pair -- both former winners of the Tiger Woods-hosted event -- walked back to the correct tee and drove off the correct marker.
Both were handed a two-shot penalty for the mistake, but had they not noticed and completed the hole, they would have been disqualified.
Stenson would eventually finish with a 72 for a second-from-last 19th place finish, while Spieth shot 76 to finish 20th.
Despite the mix up, the pair were able to laugh about the event afterwards.
"My question was if we could just finish 19th and 20th and leave after nine (holes)," Stenson said, "but that wasn't an option, either."
Spieth added: "He asked them if we could just go to the airport and I said: 'I'm down.'"
Spieth explained the comedy of errors. "I teed it up first and it wasn't my tee," the 28-year-old said. "So Michael [Greller, his caddie] told me it's not my tee. Then Henrik hit. Then I teed up too far in front and he told me to scoot back."
Realizing Spieth had just given it all away, Stenson said to Spieth: "You just spoiled the whole thing. Like, look at these guys; they don't know who's going to hit. Once they figured out who's hitting, one guy's trying to tee up in front and then they both hit from the wrong tee box. I guess we got what we deserved.
"Let's just leave it that a little note on the tee box would have been helpful and I will make sure I tee it up on the right tee box in the future because I don't think I've ever done this before. Have a nice Christmas everyone and we'll see you in the new year."
At the other end of the leaderboard, it was a day to forget for Collin Morikawa.
The American began the final round five shots ahead of his nearest challenger.
With a victory at the Hero World Championship, Morikawa would have become the world No. 1, just the fourth player to reach the top of the rankings before the age of 25, alongside Tiger Woods, Rory McIlroy and Spieth.
However, it started terribly for the two-time major winner, shooting an error-strewn, front-nine 41 to come back to the pack.