Usain Bolt was slower than Justin Gatlin in his 100 metre heat, while Christoph Harting took gold in the discus.
The Jamaican world record holder played up to the crowd and did the least he could to finish his opening race of Rio 2016 first, but Justin Gatlin was the fastest qualifier for the semi-finals.
The only gold of the day's opening session went to Harting, while Jessica Ennis-Hill was also in action on the final day of the women's heptathlon on Saturday.
BOLT NOT QUITE LIKE LIGHTNING
Bolt was greeted in rapturous fashion upon his Olympic Stadium entry. The Jamaican immediately set about his typical showman antics, with the raucous reception of his practice start drawing his applause.
When it finally came to race time, Bolt had a fairly sluggish start but coasted across the finish line in comfortable fashion, looking to his side to ensure he stayed ahead of closes rival Andrew Fisher of Bahrain.
His time of 10.07 seconds was slower than the 10.01 run by Gatlin in an earlier heat, and Bolt still has work to do to keep his triple-triple hopes alive.
-- Team Jamaica (@JamaicaOlympics) August 13, 2016
LEVELLING THE SIBLING RIVALRY
Robert Harting was the gold medal winner in the discus at London 2012, and four years later his brother, Christoph, matched his feat.
Having seen Robert fail to qualify for Saturday's final, Christoph took full advantage.
Poland's Piotr Malachowski took the lead into the final round with a throw of 67.55m on his third attempt, but the German produced a personal best of 68.37 to pip him to the gold.
THIAM OVERTAKES ENNIS-HILL
Ennis-Hill took a 72-point lead into Saturday's heptathlon conclusion, but she was overtaken at the top of the rankings by Nafissatou Thiam following the long jump.
Thiam produced a personal best jump of 6.58m with her third and final attempt, catapulting her up the event rankings and five points clear of Ennis-Hill on the overall leaderboard.
Katarina Johnson-Thompson moved into the final medal position by jumping 6.51m. The final two events of javelin and the 800m come in Saturday's evening session.
DIRO SAVED AFTER SHOE LOSS
Etenesh Diro of Ethiopia was one of the favourites to advance to the final from the third and last 3,000 metre steeplechase heat.
However, an incident in the closing stages resulted in Diro, Aisha Praught and Sara Treacy all falling, with the Ethiopian opting to remove a troublesome shoe and sock before finishing the race through sheer determination
The 25-year-old finished seventh and was helped down the tunnel, but a successful appeal ensured she would appear in the final on Monday.
Four medals will be won at the Olympic Stadium in Saturday's evening session. Greg Rutherford will be looking to defend his long jump title, while Mo Farah will attempt to do the same in the 10,000m.
A tantalising semi-final heat in the women's 100m semi-final will pit Dafne Schippers and Shelly-Ann Fraser-Pryce together, with the final following later in the night..