Graham DeLaet set the clubhouse target on day one of the Olympic Men's Golf Competition but it was Australian Marcus Fraser who was setting the pace in Rio de Janeiro.
DeLaet was aiming to make it back-to-back titles for Canada - albeit 112 years apart - after George Lyon's triumph in 1904 as golf made its eagerly awaited return to the Games.
The 34 year old opened with a five under par 66 but Fraser was one shot ahead with four holes to play as he made seven birdies on the Olympic Golf Course.
Justin Rose was three under through four holes and he wrote his own name in the history books as the Briton made the first hole-in-one in Olympic history on the par three fourth.
Local favourite Adilson da Silva had the honour of hitting the opening tee-shot on Thursday morning but it was playing partner DeLaet who made the big early impression with birdies on the third, fifth, sixth and eighth to turn in 31.
A bogey followed on the 11th but gains on the 13th and the last meant DeLaet was the man to catch.
Fraser took advantage of the par five first and, after a bogey on the next, went on a stunning run of four birdies.
An approach to four feet and excellent tee-shot set up gains on the third and fourth before the putter got hot as the Maybank Championship Malaysia winner holed from 23 and 25 feet on the fifth and sixth.
A beautiful approach to the par five tenth set up another birdie and a further gain on the 13th had Fraser six under.
Germany's Martin Kaymer had already labelled this week the "greatest of my career" before a tee-shot was hit and the two-time Major winner certainly looked to be enjoying himself at four under.
After a birdie-bogey start, he made three gains in a row and added another on the tenth.
Byeong-hun An was then at three under after a rollercoaster of a 68. An's parents both won Olympic medals in table tennis in 1988 and the South Korean showed some of that pedigree in the early stages as he recovered from a three-putt bogey on the first to turn in 31.
He was slightly more erratic on the back nine as he came back in 37 to sit three behind Fraser.
Rose was also at three under alongside Swede David Lingmerth, Australia's Scott Hend and Belgian Thomas Pieters.
Rose's team-mate Danny Willett was then at two under alongside Italy's Matteo Manassero, Paraguayan Fabrizio Zanotti and Frenchman Grégory Bourdy.
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