Spieth is listed at 6-1 at the Westgate Las Vegas SuperBook. He is the only golfer with single-digit odds and is attracting action.
More money has been bet on Spieth to win the tournament than any other golfer at the SuperBook and William Hill's Nevada sportsbook. With a strong performance, Spieth has a chance to overtake Rory McIlroy and become the No. 1 player in the Official World Golf Ranking.
McIlroy, in his first tournament back since rupturing a ligament in his left ankle in early July, isn't receiving much support from bettors. As of Tuesday, less than 2 percent of all bets placed at William Hill were on McIlroy, the defending champion. More bets had been placed on 50-1 long shot Tiger Woods to win the tournament than McIlroy.
Action had been so light on McIlroy at the SuperBook that assistant manager Jeff Sherman lengthened his odds from 8-1 to 12-1 at the beginning of week. McIlroy was 5-1 to win last year's PGA Championship at Valhalla and had single-digit odds for all three prior majors this year.
"Very minimal support for him this week," Sherman said. "He says he's 100 percent, but the only thing I would be leery of is him being away from competitive golf for a little bit of time."
McIlroy missed The Open and has not played a competitive round since the U.S. Open in late June.
Along with McIlroy, Bubba Watson and Jason Day are also 12-1. Dustin Johnson is 15-1, and Justin Rose and Rickie Fowler are 20-1.
Fowler was the most popular pick at William Hill and was second to Spieth in money wagered upon.
Woods, after missing the cuts at the U.S. Open and The Open, is a -130 favorite to make the cut this week at Whistling Straits. Only five golfers had attracted more money than at Woods at William Hill, as of Tuesday.
Phil Mickelson is 40-1 to win the tournament. John Daly is 1,000-1.
"We've got one ticket on Daly, when he was 500-1," said Sherman, who added that he bet on Day and Fowler, in addition to long shots Brooks Koepka, Justin Thomas and Danny Lee.
The SuperBook will release 2016 Masters odds next week.
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