His latest title left him equally confused, though undeniably thrilled.
With an incredible surge on the back nine of Sheshan International, Johnson played a five-hole stretch in 5-under par to pull away from Ian Poulter and Graeme McDowell and win the HSBC Champions on Sunday. His 6-under 66 gave him the tournament record (24-under 264), a three-shot win over Poulter and his first World Golf Championship.
He's just not sure where it fits in his timeline.
Johnson won the Tournament of Champions at Kapalua in January, and because the HSBC Champions is his last official tournament of the year, the 29-year-old American can claim to have started and ended 2013 with wins.
However, it also the second straight season that Johnson won the first tournament he played—even though it's the same year. The PGA Tour has gone to a wraparound season for the first time, and while 2013-14 began a month ago, this was the first one he played.
"It's been a long year, so getting off this year with a win is definitely huge," he said. "I won the first event of the year and I struggled a little bit through the end. But I've been putting in a lot of work the last month or two, and it definitely feels really good to get a win and get off to a good start this year."
Much easier to figure out was his golf.
Johnson started the final round with a three-shot lead, which was gone by the time he reached the third tee.
They were tied at 17-under, and there wasn't a lot of separation the rest of the way.
All three of them made birdie on the par-5 14th in three different ways—a two-putt from 40 feet by Poulter, the shortest hitter of the group; a 40-foot putt by McDowell that slammed into the back of the cup; and a 20-foot putt by Johnson, who figured the hole had seen enough birdies already from that group.
"That was a big putt," he said.
Poulter fell out of the lead with a bogey on the 15th from a bunker. McDowell lost hope when he twice missed birdie putts inside 15 feet. But this tournament was won. Johnson completed his big run by pitching in for eagle from just short of the 16th green, and then hitting 5-iron to 8 feet for birdie on the 17th.
"It's the biggest win I've had in my career so far," he said. "Those guys put a lot of pressure on me. I'm really proud of the way I handled myself."
It was tense and it was fun. There wasn't a lot of talking among them over the final two hours, yet the golf was at such a high standard that it was obvious all three players relished having a chance to capture this World Golf Championship.
"A little disappointed not to put my hands back on the trophy," said Poulter, who won the HSBC Champions last year at Mission Hills. "But 15 birdies and an eagle at the weekend is some pretty good golf. Dustin finished the job. It was good golf and it was good fun to play in that group."
McDowell shot 64-66 on the weekend without making a single bogey. That still left him four shots behind.
"Dustin Johnson was in a different league off the tee and gave us a little bit of a sniff, and then promptly slammed the door," McDowell said.
Even in defeat, it was an important week for both of them.
McDowell still holds out hope of winning the Race to Dubai. He remains No. 2 on the European Tour money list, though his third-place finish allowed him to significantly close the gap on Henrik Stenson, who has been struggling since capturing the FedEx Cup.
U.S. Open champion Justin Rose, who finished fifth, is third in the Race to Dubai, followed by Poulter, who made a huge jump as the runner-up in an event with an $8.5 million purse.
All of them are neighbors at Lake Nona in Orlando, Fla.
Stenson, Rose and Poulter were headed to the Turkish Open this week. McDowell was taking a week off, which will cost him a 20 percent bonus in points going into the World Tour Championship at Dubai to close out the year.
McDowell had no regrets about sitting next week out. He did the hard work Sunday to give himself a chance.
"I'll be fresh. I'll be ready in Dubai whatever happens," he said. "Just trying to give myself a shot going into Dubai."
Poulter said he was in "great form" after his 63-66 weekend. "I couldn't be hitting it any better right now," he said.
Rose was part of an all-star cast chasing Johnson. For most of the back nine, the six guys behind Johnson represented half of Europe's winning Ryder Cup team. He remains a long shot to catch Stenson, though Rose is looking forward to the next two weeks.
"Henrik probably couldn't believe the leaderboard, probably the worst possible leaderboard for him this weekend with GMac, Poults, me, and even Gonzalo (Fernandez-Castano) playing well at one point," Rose said. "So everybody is breathing do you know his neck and it's going to be an exciting Race to Dubai."
For Johnson, it was a rewarding trip home.
As for those tour wins? He won Saturday in the 2011 Barclays when it was shortened to 54 holes because of a hurricane; Monday at Pebble Beach in 2009 when the final round was canceled because of rain; and Tuesday at Kapalua because of high wind all week.