RIO DE JANEIRO (AP) – This is goodbye for Michael Phelps. The most decorated athlete in Olympic history has one more race before retirement.

His shot at a 28th medal comes Saturday in the final slate of swimming at the Rio de Janeiro Games, where Usain Bolt, the fastest man in the world, made his first appearance at the Olympic Stadium.

With four gold medals at these games and 22 for his career, Phelps needs some help from his teammates to win another – he leads off with the butterfly leg of the 400 medley relay.

There are 22 golds at stake on a sun-splashed Day 8 of the Rio Games in 13 sports, including fencing, track cycling, boxing, shooting, trampoline and weightlifting.

While competitions wrap up in swimming and rowing, they’re just heating up in track and field, which will award five golds: for the women’s 100 meter sprint and the heptathlon, and the men’s 10,000 meters, discus and long jump.

Bolt turned the Olympic Stadium into his stage again for his first race at the Rio Games, cruising to an easy win in his 100-meter heat, backed up by the trademark showmanship to the thrill of the crowd.

Andy Murray , the singles tennis champion in London four years ago, moved into the Rio Games final by easily beating Kei Nishikori of Japan 6-1, 6-4 on Saturday. He’ll face either Rafael Nadal of Spain or Juan Martin del Potro of Argenia in Sunday’s final.

Phelps was beaten in his last Olympic individual race Friday night by a 21-year-old who grew up idolizing him. Joseph Schooling of Singapore built a big lead in the 100-meter butterfly and easily held off one of Phelps’ patented rallies.

Speaking of comebacks, Phelps insists he won’t be coming out of retirement again to take on Tokyo in 2020.

“I’m not going four more years and I’m standing by that,” Phelps said. “I’ve been able to do everything I’ve ever put my mind to in the sport and after 24 years in the sport, I’m happy with how things finished.”