Golf made a dramatic return to the Olympic Games after 112 years on Thursday with Briton Justin Rose hitting a hole-in-one, ahead of Michael Phelps' bid for a 22nd gold medal.
Germany won three titles to ease home fears and another new sport, rugby sevens, headed for a tense climax with Fiji, Japan, Britain and South Africa in contention.
Brazilian Adilson da Silva hit the first Olympic golf shot since Canada's George Lyon won at St. Louis in 1904, which landed in a fairway where a crocodile lurks.
Other traps are waiting for the sport. But former US Open champion Rose's hole-in-one on the 188 yard fourth hole was an early highlight.
Reigning British Open champion Henrik Stenson of Sweden and 2016 Masters champion Danny Willett of England were among six major winners in the field of 60 seeking a gold medal.
But the world's four top players -- Australia's Jason Day, Americans Dustin Johnson and Jordan Spieth and Northern Ireland's Rory McIlroy -- were among about 20 top stars who skipped Rio.
Many cited concerns over the zika virus. But some sceptics say Zika was a convenient excuse with the US PGA Tour's season-ending playoffs starting days after Rio ends.
And the International Olympic Committee has said it will evaluate the number of "stars" at each sport in deciding whether it gets a place beyond Tokyo 2020.
Germany has been fretting over its lack of success in Rio but struck gold in the in the men's and women's quadruple sculls and shooting to zoom up the medals table with four in all.
The men's crew of Phillipp Wende, Lauritz Schoof, Karl Schulze and Hans Gruhne defended their title in the men's quadruple sculls
Moments later Annekatrin Thiele, Carina Baer, Julia Lier and Lisa Schmidla claimed the women's title. Barbara Engleder won the 50m rifle three position contest for Germany's first gold in Olympic women's shooting.
Forty-year-old rower Katherine Grainger became Britain's most decorated Olympic woman athlete with a second place in the double sculls with Victoria Thornley, her fourth silver in five Olympics. The pair were narrowly beaten by Poland's Natalia Madaj and Magdalena Fularczyk-Kozlowska.
Dominant New Zealanders Eric Murray and Hamish Bond stretched an eight-year unbeaten streak in the men's pairs.
Fiji guaranteed itself of a first Olympic medal by cruising past Japan 20-5 to reach the final of the rugby sevens, making its first appearance at the Olympics.
They will face Britain in the gold medal clash later Thursday after they defeated South Africa 7-5 in the other semi-final.
The curtain comes down on one of swimming's great rivalries when Olympic giant Phelps and Ryan Lochte lock horns one last time.
Phelps will look to win the men's 200m individual medley for an incredible fourth successive Games while Lochte finally tries to get one over on his fellow American.
"The history him and I have had with one another it's something special," said Phelps, who won his record 20th and 21st Olympic gold medals on Tuesday.
"We've been racing for the last 12 years and having one more battle tomorrow will be fun," he added after qualifying quickest for the final on Wednesday.
Australian sisters Cate and Bronte Campbell will clash in the women's 100m freestyle final.
And there could be tension in the women's 200m breaststroke when American Lilly King, who won gold in the 100m breaststroke, clashes again with two-time doping offender Yulia Efimova of Russia.
Meanwhile, a Namibian boxer arrested for alleged sexual assault at the athletes village will fight as scheduled on Thursday, officials said.
Jonas Junias Jonas, 22, was detained on Sunday for allegedly assaulting a female room cleaner in the second sex case to rock the Games village. Jonas weighed in for the competition on Thursday.