Phil Mickelson, left, and Dustin Johnson, right, join Rory McIlroy in one of the more swashbuckling first- and second-round pairings of the 111th U.S. Open at Congressional Country Club. (Scott Halleran/GETTY IMAGES)

Graeme McDowell will begin defense of his U.S. Open crown Thursday at Congressional Country Club in the traditional grouping of the reigning trophy-holder with the defending U.S. Amateur and British Open champions — in this case, Peter Uihlein and Louis Oosthuizen, respectively.

But the marquee attraction when play begins in the 111th Open: The risky, daredevil grouping of Phil Mickelson, Dustin Johnson and Rory McIlroy, perhaps the most intriguing of 52 threesomes who will play the first two rounds together.

Mickelson, a four-time major champion, will join Johnson, who led the Open through 54 holes last year, and McIlroy, a 22-year-old Northern Irishman from whom much is expected, from the 10th tee at Congressional’s Blue Course at 1:35 p.m. in Thursday’s first round. That threesome will then play the second round from the first tee at 7:55 a.m. Friday. The group is likely to be featured in ESPN’s prime coverage Thursday afternoon into the evening.

Each group will play once in the morning and once in the afternoon, and each will begin either the first or second round from No. 1, and the other from No. 10, a par-3 over water, which is an unusual way to start a golfer’s day. The United States Golf Association, which stages the Open, has been using the two-tee format, typical on the PGA Tour, since the 2002 Open at Bethpage Black.

McDowell’s defense of the title he won at Pebble Beach will begin from the first tee at 7:55 a.m. Thursday. He will be joined by Uihlein, a junior at Oklahoma State who is the top-ranked amateur in the world, and South Africa’s Oosthuizen, who surprisingly dominated the British Open field at St. Andrews a year ago.

The last three top-ranked players in the world — Luke Donald, the current No. 1, and Lee Westwood, both of England, and Germany’s Martin Kaymer — will play together in the first two rounds, as will three recent Masters champions: Charl Schwartzel (2011) and Trevor Immelman (2008), both of South Africa, and Zach Johnson of Iowa (2007).

Two other groupings will bring together past major champions: Ernie Els, who won the most recent Open held at Congressional in 1997, will be joined by Americans Davis Love III, winner of the 1997 PGA Championship, and Jim Furyk, who won the Open in 2003. The group of Irishman Padraig Harrington, Argentina’s Angel Cabrera and American Stewart Cink has six major championships among them.

The USGA created some interesting international groupings for this Open as well. Spaniards Miguel Angel Jimenez, Sergio Garcia and Alvaro Quiros will play together in the first and second rounds as will Italians Matteo Manassero and brothers Edoardo and Francesco Molinari.