Although overshadowed by the ''big three'', Richardson came to South Korea in fine form after winning the Stockholm Diamond League meet in late July, where he beat US teammate Oliver.
At the London Diamond League meet earlier this month he was second behind Robles but again finished ahead of Oliver.
And, sneaking under the radar, Richardson, who won the 110m and 400m hurdles double at the 2003 world youth championships, looked strong in qualifying in Daegu.
The disqualification of Robles also meant Liu, the 2004 Olympic champion and former world record holder, who timed 13.27sec, was promoted to silver from bronze with Britain's Andy Turner taking bronze (13.44sec).
All had earlier seemed straightforward as a delighted Robles played down the contact with Liu, saying: "That's normal in hurdles. I feel great."
Giving his version of the incident, Liu said: "I felt like someone touched my elbow and I lost my balance for a while but then I managed to stabilise it. It happens all the time in competitions but this time, in the final of the world championships, it was kind of different.
"I'm sorry this happened to him because he's a friend of mine."
Oliver, who owns the fastest time in the world this year (12.94) was never in contention, finishing fourth in a photofinish with Turner following Robles'' disqualification.
He defended his Cuban rival on Twitter, saying Robles had lost balance after clipping a hurdle. "People who think Robles did it on purpose are crazy and haven't seen his races, late in races he's been getting wide with his arms.
"Gotta feel bad for Liu as his lead leg was ahead of Robles when the last contact over 10 happened between them, all around bad situation," he said.
PTI