Genesis Open: As tournament host, finished 6-under and T15 in the Genesis Open, the only event on TOUR at which he has made double-digit starts and not earned a victory. Now has seven top-15s in 13 starts in this event. Made a 43-foot, 10-inch eagle putt at No. 1 in the second round, marking his longest putt made on TOUR since 2014 WGC-Mexico Championship. Played his first four holes of the third round 5-under (B-E-B-B) en route to a 6-under 65.
Chevron World Challenge: Lost in a playoff to Graeme McDowell at the Chevron World Challenge. It was the first time as a professional that he lost after holding a three-shot-or-more lead entering the final round. McDowell drained a 20 foot putt on the 72nd hole to force a playoff and then made a 25 foot putt on the first playoff hole (No. 18) to capture the win. The world's No. 2-ranked player missed a 14-foot putt that would have extended the playoff. He has finished in the top two at this event in eight of his 10 starts.
World Golf Championships-American Express Championship: With victory at the World Golf Championships-American Express Championship, became the first player in TOUR history to win five times in five consecutive seasons. Captured his record fifth consecutive Byron Nelson Award and the PGA of America's Vardon Trophy, based on each player's adjusted scoring average. Finished the season with an adjusted scoring average of 68.41, the second-lowest in TOUR history.
the Memorial Tournament presented by Nationwide Insurance: Moved into a tie with Jack Nicklaus for second on the all-time PGA TOUR victories list, with 73, after his two-shot victory at the Memorial Tournament. Trails only Sam Snead's 82 wins after a two-shot victory over Andres Romero and Rory Sabbatini at Muirfield Village GC. Posted his 73rd career victory at age 36 years, 5 months, 4 days, nearly 10 years younger than Nicklaus when he won his 73rd tournament (46 years, 2 months, 23 days) and almost seven years younger than Snead when he posted his 73rd victory (43 years, 9 days). Collected his fifth career victory at the Memorial Tournament and won in come-from-behind fashion for the 21st time in his career after entering the final round four shots off the 54-hole pace. Trailed Sabbatini by two shots standing on the 15th tee but played his final four holes in 3-under, making birdie on Nos. 15, 16 and 18. Holed a flop shot from 49 feet, 10 inches from behind the green at the par-3 16th to tie Sabbatini for the lead at 8-under. Won the Arnold Palmer Invitational and the Memorial Tournament in the same year for the fourth time (2000-01, 2009 and 2012). Posted the 12th victory of his career in Ohio and won multiple tournaments in a season for the 13th time in his career.
Hero World Challenge: Hero World Challenge host finished T9 and 10 strokes behind champion Rickie Fowler. Marked his first appearance in competition since withdrawing from the Omega Dubai Desert Classic on February 2, 2017. Week included playing in the first and final round with reigning FedExCup champion and PGA TOUR Player of the Year Justin Thomas, with both players posting scores of 69-68 in those rounds.
Surgery: Pulled out of next two PGA TOUR starts, the Genesis Open and The Honda Classic. Released statement: "My doctors have advised me not to play the next two weeks, to continue my treatment and to let my back calm down. This is not what I was hoping for or expecting. I am extremely disappointed to miss the Genesis Open, a tournament that benefits my foundation, and The Honda Classic, my hometown event. I would like to thank Genesis for their support, and I know we will have an outstanding week." In April, announced on his website he had undergone further back surgery. The operation was performed by Dr. Richard Guyer of the Center for Disc Replacement at the Texas Back Institute.