Defending champion Graeme McDowell battled to a level par 72 on the opening day of the Northwestern Mutual World Challenge.
McDowell outscored playing partner Rory McIlroy by a single shot at Sherwood County Club in California.
American Zach Johnson grabbed an early lead in the limited field event with an opening round 67.
Meanwhile, Simon Dyson has been given a two-month ban from the European Tour, suspended for 18 months, but was cleared of “a premeditated act of cheating” on Thursday.
Dyson was joint second after 36 holes of the BMW Masters in October when he was disqualified for signing for an incorrect score in the second round.
The 35-year-old failed to add a two-shot penalty to his card after an incident on the eighth hole at Lake Malaren, when he touched the line of his putt after marking his ball, using the ball to flatten a spike mark.
Having reviewed the incident after being alerted to it by television viewers, European Tour officials charged Dyson with a “serious breach” of the Tour’s code of behaviour, a charge which was upheld when the Yorkshireman appeared before a three-person disciplinary panel at Wentworth.
The panel found that Dyson deliberately pressed down the spike mark to improve his position, despite knowing it was against the rules.
The six-time European Tour winner was also fined £30,000 and ordered to pay £7,500 towards the Tour’s costs, with the money to be paid within 56 days.
Dyson declined to make any comment on the ruling.