Kansas City (4-1), which closed as a 10½-point favorite, suffered its first loss of the season in a 19-13 defeat to Indianapolis on Sunday night at Arrowhead Stadium.
The four-time major champion is the 8-1 favorite to win the year’s final major at Royal Portrush, where he has the course record, in his native Northern Ireland.
The Westgate and William Hill sportsbooks had six figures of liability on Tiger Woods and Phil Mickelson, and neither golfer threatened.
The six-time runner-up was 30-1 at the Westgate as of Tuesday afternoon for the tournament, which begins Thursday at Pebble Beach. Dustin Johnson is the favorite at 7-1.
The day after the prop was posted at the Westgate sportsbook, a bettor placed a $5,000 wager to win $6,500 on Koepka to go over 7½ majors at plus 130.
The golfer misses the cut Friday at the PGA Championship, and sportsbooks won’t have to sweat out a large number of bets that he would win the 2019 Grand Slam.
The Masters champion is the 8-1 favorite to win the PGA Championship, the year’s second major, which begins Thursday at Bethpage Black in New York.
The 15-time major champion is the 8-1 favorite to win the PGA Championship and a 20-1 shot to have the lead after Thursday’s first round at Bethpage Black in New York.
There’s little value in his 8-1 odds, so golf handicapper Brian Blessing will look at Sergio Garcia at 50-1 and six others to win the second major of the year.
Wisconsin resident James Adducci placed a $100,000 bet at SLS Las Vegas on Wednesday on the golfer to win the next three majors at 100-1 odds and complete the 2019 Grand Slam.