RIO DE JANEIRO >> 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.”

Other highlights from Day 8:

SLUGGISH SPRINTER : Bolt did not disappoint the crowd, but he was displeased with himself. He was slow out of the blocks but once his tall majestic frame reached full flow, there was no stopping him. “It wasn’t the best start, it felt kind of sluggish,” Bolt said, adding that he never has been a morning person and preparations for his noon-time race felt unusual. “I’m not used to running this early in the morning in any championships.”

GOODBYE GREEN : They’re going to drain what’s been dubbed “the swamp” at the Rio Olympics. The water at the Maria Lenk Aquatics Center has been green-tinged and murky for five days. Officials blame the green water on algae, poor maintenance, heat and more swimmers than expected using the facility. Organizers have insisted the water is safe though some athletes have complained about their itchy eyes.

MILLENIAL MEDAL : Sometime very soon, possibly even later Saturday, the United States will lay claim to its 1,000th overall gold medal in the Summer Olympics. Although counting them has proven an inexact science, the U.S. Olympic Committee says the official count coming into the Rio Games was 977 golds, a global high. James Connolly won the first for the U.S. in 1896, and of course no one has added more to the total than Phelps.