At US Open, the real money is off the golf course

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Jordan Spieth of the United States plays his shot during a practice round prior to the U.S. Open at Oakmont Country Club on June 13, 2016 in Oakmont, Pennsylvania.

The U.S. Open tees off in Oakmont, Pennsylvania, this week. The purse for the tournament is $10 million, but in terms of income, it barely matters who wins the 116th playing of the championship.

That's because less than 30 percent of the total income earned by the PGA's top 50 players came from playing golf last year, according to data from Golf Digest, which tracks earnings on and off the course. Thirty-three of the those 50 earners made more money off the course.

Look at Tiger Woods, for example. The man who made golf cool — and profitable — earned just $550,000 playing the game in 2015, and $48 million on endorsement deals off the course. Amazingly, Woods isn't at the top of the list in terms of total earners. For the first time in the 13 years Golf Digest has collected the data, Woods dropped to the third spot, behind Phil Mickelson and 22-year-old Jordan Spieth.

Spieth earned $23 million in prize money in 2015 and an additional $30 million in endorsement deals. He's defending his U.S. Open championship this year, having picked up $1.8 million in his 5-under-par nail-biter last year.

Mickelson, who turns 46 on Thursday, earned just $2.3 million on the course and $50 million off.

Spieth's age is indicative of a big trend in the top 50 earners list: They're young. Many of the top earners were inspired by Woods to get into golf in the first place. After all, he was one of the first players to show you could make real money playing well and making endorsement deals off the course.

Think back to 1995. That's the year before Woods went pro and the PGA Tour money list was topped by Greg Norman, with $1.6 million. Compare that with Spieth's $23 million on-course income last year. And Woods himself has made over $1.4 billion in the past 20 years.

Still, the total earned by the top 50 players has actually dropped since 2014, when they made $650 million. Last year, that figure was just $637 million. But the loss was entirely on the on-course side, which dropped from $208 million to $186 million. Earnings from endorsements rose $10 million, to $451 million.

Woods' departure from the top of the list may mark the end of an era, but a lot of young players are moving up. Many of the 17 who earned more than half their income on the course are bright young stars like 25-year old Danny Lee (ranked 46) and Lydia Ko (ranked 47), who is just 19.

In a post-Tiger time, every young golfer is only a few endorsements away from multimillion dollar paydays off the green.