Dustin Johnson shot -7 to take the clubhouse lead, with Jordan Spieth finishing on -5.
Dustin Johnson has the clubhouse lead at the 144th Open Championship.
The American made five birdies on his 18 holes and one eagle to set the pace at St Andrews with a score of -7.
Masters and US Open champion Jordan Spieth partnered Johnson along with Hideki Matsuyama and finished on -5, making an impressive birdie on the final hole.
Jason Day, Paul Lawrie and Retief Goosen all finished one shot back of Johnson, while amateur Jordan Niebrugge leads the race for the silver medal after a round of 67.
Watch Dustin Johnson discuss the Old Course
Louis Oosthuizen, winner of the last Open at St Andrews five years ago, also shot 67.
David Lingmerth birdied seven of the first nine holes, but made three bogeys and one double bogey on the back nine.
Tiger Woods continued his inconsistent form this year by shooting a 76, the same score as Tom Watson, who is making his final Open appearance.
It was a mixed day for the Englishmen in the field, with Luke Donald and Greg Owen setting the pace after carding rounds of 68.
Ian Poulter finished +1 after making two bogeys and just one birdie, with Lee Westwood and Ross Fisher both scoring 71.
There were a number of strong performances from the amateurs in the field, with Paul Dunne and Romain Langasque both shooting 69.
Dunne was one of the early starters and rolled in an incredible putt from over 100ft on the back nine.
Oliver Schniederjans finished on -2 to give himself a strong chance of making the weekend cut.