U.S. Open: 5 storylines to follow this week at Oakmont

The U.S. Open tees off Thursday, and the world's best golfers have their eyes on one of the most coveted titles in the sport and a $10 million US purse.

Established in 1895, the U.S. Open is the second-oldest major championship on the PGA Tour after the British Open.

Here are five storylines to watch as the tournament returns to Oakmont Country Club for the first time since 2007.

The crazy course

Oakmont, located northeast of Pittsburgh, is known as one of the most difficult courses to play in golf due to its sheer size and complexities. For example, the first hole is an extremely narrow 482-yard par-4.

In 2007, 37-year-old Angel Cabrera of Argentina won the tournament with a total score of 5-over par. He was the only player with multiple rounds in the red, opening and closing with a 1-under 69.

The Big Three

Jason Day, Jordan Spieth and Rory McIlroy — ranked No. 1, 2 and 3 in the world, respectively — are considered the favourites to win this weekend. Day is the only one of the bunch who has not won the U.S. Open, although he did finish second behind McIlroy in 2011.

Day has won three PGA Tour events this year, including the Players Championship. Spieth has taken home two titles in 2016, but also finished tied for second at the Masters after a final-round collapse. Meanwhile, McIlroy is coming off a strong performance at the Memorial Tournament, where he finished tied for fourth.

The thrill of Phil

Phil Mickelson is riding high into this year's U.S. Open. The 45-year-old lefty just finished tied for second at the most recent PGA event — the St. Jude Classic.

Mickelson has won every major championship in golf aside from the U.S. Open, including three victories at the Masters. This year's event at Oakmont is a prime opportunity for the American to finally win his national championship.

The eyes on DJ

Dustin Johnson is one of the world's best golfers — he's just had some difficulties proving it in a major. Last year at Chambers Bay, Johnson had an excellent opportunity to win the U.S. Open with an eagle try from 15 feet away on the 18th green. Instead, he three-putted and watched Spieth bask in glory.

This year, the 31-year-old American will try again to take home the title as the No. 6-ranked golfer in the world. Since last November, Johnson has finished tied for fifth place or better in six tournaments.

The Spaniard

Sergio Garcia joined the PGA Tour in 1999 but has never been able to win a major. The Spanish golfer was highly touted as a youngster at the same time Tiger Woods was on top of the world of golf. Now, at the age of 36, Garcia could open some eyes at Oakmont with a victory.

Ranked No. 13 in the world, Garcia won the Byron Nelson tournament last month and finished second at the Honda Classic in February. A win on Sunday would go a long way toward changing how he is remembered in golf history.