US runner Richards got her first global title in the women's 400 metres on Tuesday and the retirement-bound Nerius did the same in the javelin, the first gold for hosts Germany in Berlin.
Kemboi continued a proud Kenyan 3,000 metres steeplechase tradition with his first title after three previous runner-up finishes.
Kerron Clement of the US defended his 400m hurdles title, Phillips Idowu followed in the footsteps of Jonathan Edwards with triple jump gold for Britain, and Usain Bolt jogged into the 200 metres semis.
Richards, 24, led from start to finish en route to a winning 2009 world best 49.00 seconds.
Shericka Williams of Jamaica got silver like at the 2008 Olympics in a personal best 49.32 seconds. Antonina Krivoshakpa of Russia took third place with 49.71 seconds
"To come here and to win the race, it means the world to me. Finally, I have own a major title! Finally the hard work has paid off. Before, I had difficulties standing the pressure. But now I am a better athlete," said Richards.
Richards was the dominant 400m runner over the past years, but failed to qualify for the 2007 worlds and then tired dramatically on the home stretch at the 2008 Olympics to finish third.
Richards is suffering from Behcet's syndrome, a rare illness that causes chronic inflammation of blood vessels in the body which had led to the disappointments of the past.
"It flared up a little bit here because it comes when I am stressed. But I now know how to handle it," she said.
The defending champion and Olympic gold medallist Christine Ohuruogu of Britain was no factor in fifth place.
Kemboi proved strongest on the home stretch to win the steeplechase in a championship record 8:00.43 minutes from compatriot Richard Kipkemboi Matelong, who had 8:00.89.
Frenchman Bouabdellah Tahri denied Kenya a second straight sweep at the worlds, stealing the bronze on the finish line by eight hundredth of a second from Paul Kipsiele Koech with a European record 8:01.18.
Kemboi won Olympic gold in 2004, but had never managed to top a podium at worlds, coming second in 2003, 2005 and 2007.
"I stayed patient and I reached my target. It is a great time for me in Berlin," said Kemboi.
Defending world champion and 2008 Olympic champion Brimin Kiprop Kipruto of Kenya had to settle for seventh place while Moroccan Jamal Chatbi was kicked out before the final, testing positive for the steroid clenbuterol at an out-of-competition test on Saturday.
Nerius got a gold at last after bronze at the last three worlds and an Olympic silver in 2004, shocking the opposition with an opening round throw of 67.30m which proved good for gold.
Czech world and Olympic champion Barbora Spotakova had to settle for second with 66.42m and Maria Abakumova of Russia was third with 66.06m.
"The is the greatest and most beautiful moment of my life, winning the world championship gold at home in my farewell season," said the 37-year-old Nerius.
Idowu beat world and Olympic champion Nelson Evora of Portufal with a huge third-attempt leap of 17.73m in which he did not even hit the board -- thus wasting some 20cm in what was still a personal best.
Evora came second with 17.55m and Alexis Copello of Cuba got bronze with a final attempt of 17.36.
In the hurdles, Clement surged to his second world title on the home stretch in a world leading 47.91 seconds. Javier Culson of Puerto Rico came second with 48.09m and Bershawn Jackson added bronze for the US in 48.23.
Bolt, 22, shut down after little more than half of his second round race as he won his second round in 20.41 seconds. Fellow-Jamaican Steve Mullings (20.23) and 2004 Olympic champion Shawn Crawford of the US (20.37) were among those with faster times
into Wednesday's semi-finals.
But Bolt had to conserve some energy in what was his sixth race in four days. Bolt won the 100m on Sunday in a stunning world record 9.58 seconds and said he was ready to attack his world record 19.30 seconds from the 2008 Olympics in Thursday's final.
"I feel a little tired," he said. "I am taking it round by round, but in the final I will be running hard."