Rather than play college golf, O'Hair turned professional in 1999 after his junior year at high school at Brophy College Preparatory in Phoenix, Arizona, under the direction of his father, Marc O'Hair,[2] who sold his share of the family shutter business in Lubbock for $2.75 million to develop Sean into a touring pro.

The elder O'Hair moved the family to Florida and enrolled Sean in the David Leadbetter Golf Academy.

A featured article by Steve Elling in the January 21, 2005 Golf World alleged: Marc O'Hair, 52, signed management contracts with his son, says he invested $2 million in his boy's professional future and subjected Sean to a physical and psychological regimen that would make most drill sergeants blush.

He won his maiden PGA Tour event at the John Deere Classic and finished second at the EDS Byron Nelson Championship.

After he established himself as the front-runner for Rookie of the Year distinction with his strong finish at the EDS Byron Nelson Championship and victory at the John Deere Classic, his estranged relationship with his father, already highlighted on a 2002 episode of 60 Minutes,[4] became well-publicized.

In March 2006, O'Hair was the youngest man in the top 50 of the Official World Golf Rankings but his 2006 season was less successful.

On May 12, 2007, at The Players Championship at the TPC at Sawgrass, O'Hair led Phil Mickelson by a stroke after the 3rd round.

O'Hair did not have any more notable results until the fall season series of events where he recorded consecutive top-5 finishes at the Fry's Electronics Open and the Ginn sur Mer Classic.

He shot a 63 in the third round to shoot up the leaderboard, but on the final day he finished three back of the champion Tiger Woods.

O'Hair then had his best showing at the WGC-Accenture Match Play Championship where he reached the quarter final stages, beating Adam Scott and Ian Poulter along the way, before losing to eventual finalist Paul Casey 4&3.

[5] After his win at Quail Hollow, O'Hair had a quiet spell during the middle of season but returned to form at the right time when the FedEx Cup playoffs came around.

O'Hair again opened the season with a solid performance in Hawaii at the Mercedes-Benz Championship, achieving a fourth-place finish.

O'Hair did not make into the tour finale at East Lake and finished the season ranked 47th on the FedEx Cup standings.

He was ranked well outside the top 125 after The Open Championship in July and his season best at that point was a tie for 16th place at Colonial.

WD = Withdrew QF, R16, R32, R64 = Round in which player lost in match play "T" = tied Note that the HSBC Champions did not become a WGC event until 2009.