Enjoyed a stellar rookie season, with seven top-10 finishes and a 32nd-place finish in the FedExCup standings that led to him winning PGA TOUR Rookie of the Year honors. Finished inside the top 30 on the money list to qualify for the Masters and the U.S. Open. Played in first three Playoff events, slipping from 21st to 32nd and out of the TOUR Championship.
On August 26, 2018, he won The Northern Trust for his first playoff victory; in the process, he established a new record for the tournament when held at the Ridgewood Country Club, with a score of 266, besting the old Ridgewood record of 270, which was set in 2014 by Hunter Mahan. The following week, he won at the Dell Technologies Championship played at TPC Boston in Norton, Massachusetts, with a final score of −16, two shots clear of Justin Rose. This put him over 2000 points ahead of the second place player, Dustin Johnson, in the FedEx Cup rankings. This margin secured him top seeding at The Tour Championship, regardless of his finish at the BMW Championship. This also marked his fourth win on tour, third for the year, and second during the playoffs. At the Tour Championship, DeChambeau finished 19th out of 30 participants. As a result, he fell to 3rd in the FedEx Cup, winning $2,000,000.
Hyundai Tournament of Champions: Finished T6 in a Monday-start-Tuesday-finish event, the season-opening, 54-hole Hyundai Tournament of Champions. The event "started" twice during the regularly scheduled first round Friday and later Sunday, but both times PGA TOUR rules staff halted play due to unplayable windy conditions and subsequently voided all scores that had taken place. As the first player off the tee, he ended up hitting three "opening" shots of the season.