They've already dueled in a PGA Tour playoff, where Fowler prevailed in 2012 at the Quail Hollow Championship to capture his only PGA Tour title.
And Saturday afternoon, they were on track to be grouped together in the final round of the Open Championship with the Claret Jug on the line.
In 2007, they were 18-year-old amateurs, with Fowler playing for the United States and McIlroy part of the Great Britain & Ireland team. The Walker Cup is played every two years and is similar to the Ryder Cup, although it's contested over just two days.
The two were involved in one match, with Fowler and Billy Horschel defeating McIlroy and Jonathan Caldwell 2 and 1 in Sunday's morning foursomes. It was an important point for the Americans, as the U.S. won the competition 12½ to 11½.
The match was played at Royal County Down, in McIlroy's native Northern Ireland.