Middle-distance great David Rudisha hopes Saturday's Diamond League meet in Shanghai is the start of a new odyssey in a glittering journey aimed at taking world gold in London this summer and a third Olympic title at Tokyo 2020.

The Kenyan made his Shanghai Diamond League debut last May, finishing fifth, but went on to retain the 800m Olympic title in Rio in some style.

Now his immediate focus is retaining the gold he won last year in Beijing when the world championships roll into London in August.

"In Rio, I made history, established myself as a true legend winning my second Olympic gold. Now I want to go on until the 2020 Games. That journey starts in Shanghai," the 28-year-old said on Monday from the Kenyan city of Eldoret.

Rudisha leads a field of elite runners opening their season in Shanghai as he gears up towards his world-title defense in three months' time. He is one of four 2015 Beijing champions looking for some early pointers for London.

"It's not the triumph but the struggle that matters," Rudisha added. "How you train, your focus and targets are crucial and that is what interests me. I want to do well in Shanghai; they have great fans in China."

Four years ago, two-time world champion Rudisha injured his knee while training in New York and was forced to forfeit his title defense at the 2013 worlds in Moscow.

After knee surgery, he did not race for 12 months, and upon his return in late 2014 was a shadow of his former self.

Rudisha was a haunted figure as he struggled that season with three race defeats, one of which he finished last of the pack.

But he slowly built up his strength, changing his tactics to win both in Beijing and Rio.

"I'm really happy with my progress," he said. "The win in Beijing meant a lot to me. I went to China not in the best of fitness. I wasn't at the top of the world, I wasn't the favorite. I was an underdog. That worked on my side as I had little pressure. People were not focusing on me but the other guys. I sneaked in without a lot of pressure."

The 800m world-record holder leads compatriots Kipyegon Bett, Ferguson Rotich, Robert Biwott and Alfred Kipketer in the quest for points against Poland's duo of Adam Kszczot and Marcin Lewandowski, while Zhang Dashan is the top runner from China in the two-lap race.

Xinhua