Spaniard Jon Rahm shot a magnificent seven-under par 64 at Congressional to take the first-round lead on his professional debut in the Quicken Loans National.

The 21-year-old, who was the only amateur to make the cut in last week's US Open at Oakmont, made seven birdies in a bogey-free round on Thursday.

"I wasn't cruising, but it was obviously a good day," Rahm told the PGA Tour website.

"I was really comfortable on the tee with the driver, hitting it good and hitting it straight. That allowed me to be a bit more aggressive and it paid off today."

Rahm is one shot clear of Venezuelan Jhonattan Vegas, with a group of eight players, including South African Ernie Els who turned professional five years before Rahm was born, tied on five-under par.

Els won the 1997 US Open at Congressional and told reporters: "Winning a major at a special place like Congressional, playing here again, you just keep thinking back on shots.

"Almost every single hole there's a moment back in '97 where we can remember still."

"I felt comfortable with my swing this week. I've had a very tough year. I haven't played very well, so I need to start playing well."

There is another group of 11 players just a shot further adrift on four under.