The hot favourite clocked an Olympic record of 12.35 to edge out the USA's defending champion Dawn Harper into silver by just 0.02 seconds. Another USA athlete, Kellie Wells, took the bronze in 12.48.
Pearson endured a nervous few moments before the result was confirmed on the scoreboard, bringing cheers of delight from the Australian fans.
Later, Algeria's Taoufik Makhloufi claimed men's 1500m gold in convincing fashion as he pulled clear down the home straight to win in 3:34.08. American Leonel Manzano took the silver and Moroccan Abdalaati Iguider the bronze.
Germany's Robert Harting took gold in the Discus with a throw of 68.27m. He celebrated in style by removing his top and embarking on a lap of honour draped in the German flag, before leaping over the barriers set out for the 100m Hurdles final to cheers from the stands. Iran's Ehsan Hadadi took silver with 68.18m and Estonia's Gerd Kanter bronze with 68.03m.
Ivan Ukhov took the High Jump gold medal after being the only man to clear 2.36m and 2.38m.
In the morning, Usain Bolt began his bid to add a second Olympic Games 200m crown to his two 100m titles with a comfortable heat victory.
The Jamaican, who clocked an Olympic record 9.63 to retain his 100m crown on Sunday, cruised to victory in 20.39.
Bolt has said he needs to win 200m gold again before he achieves his aim of becoming a 'legend'.
'It was an easy run, I'm enjoying it, it's my favourite event,' said Bolt.
His countryman and training partner Yohan Blake also breezed through, slowing down well before the line to clock 20.38.
World number one Aries Merritt qualified impressively in the men’s 110m Hurdles in 13.07 but there was more Olympic Games disappointment for China's Liu Xiang.
The Athens 2004 champion, one of the favourites for the gold medal in London, suffered a recurrence of an Achilles injury and was unable to make it over the first barrier in his heat.
The disappointment echoed that of four years ago when Liu - the face of the Beijing 2008 Games - stunned the crowd by walking off the start line, unable to run because of an Achilles problem.
'I feel really sorry about this situation,' said Feng Shuyong, the Head Coach of the Chinese Athletics team. 'We think it was like four years ago, the same thing happened again.
'I feel really sad because he has worked very hard to get back to the level he was at before as champion.'
Chris Hoy and Laura Trott won their second gold medals of London 2012 as Great Britain equalled their Beijing 2008 Track Cycling haul of seven wins from 10 events - but there was no golden goodbye for Victoria Pendleton.
Hoy won the final event of the London 2012 Track Cycling programme with a stunning triumph in the men's Keirin, while Trott won the women's Omnium.
But Pendleton was denied a final flourish as perennial rival Anna Meares of Australia claimed women's Sprint gold with a dramatic 2-0 win over the Briton.
There was further success for the host nation in the men's Triathlon, with Alistair Brownlee winning gold and his brother Jonny bronze. Spain's Javier Gomez finished second for silver.
At Weymouth and Portland, Spain's Marina Alabau Neira won gold in the women's RS:X with Dutchman Dorian van Rijsselberge claiming the men's event.
And in Gymnastics, China's Feng Zhe won the men's Parallel Bars crown with his compatriot Deng Linlin taking the women's Balance Beam and Epke Zonderland of Netherlands the men's Horizontal Bars.
The USA's Alexandra Raisman won gold in the women's Floor final. Raisman followed up her bronze on the Beam with an impressive performance to score 15.600 and claim the title ahead of Romania's Catalina Ponor in silver (15.200) with Russian Aliya Mustafina taking bronze (14.900).
Great Britain's Dressage riders won gold and landed their first title in Olympic Games history. Barely 24 hours after the British Jumping team clinched a first gold medal for 60 years, the Dressage trio of Carl Hester, Laura Bechtolsheimer and Charlotte Dujardin also triumphed at Greenwich Park.
China closed on a second successive clean sweep of Table Tennis Olympic gold medals as Ding Ning, Li Xiaoxia and Guo Yue overcame Japan in the women's Team event final at the London 2012 Games.
Kim Hyeonwoo became the first Republic of Korea athlete to win gold in Greco-Roman Wrestling after he beat Hungary's Tamas Lorincz in the 66kg division.
Kim had stunned the crowd by defeating reigning champion Steeve Guenot in the semi-finals and he registered an impressive 1-0, 2-0 win over his opponent in the medal showdown.
Iran's Ghasem Rezaei won the 96kg crown and there was also Iranian joy in the Weightlifting with Behdad Salimikordasiabi taking the gold in the men's + 105kg.
Brazil and Mexico will compete for the gold in the men's Football final after winning their semi-final clashes. Mexico hit back to beat Japan 3-1 while Brazil proved too strong for Republic of Korea, winning 3-0.
Russia's Ilya Zakharov ended China's Diving dominance as he claimed gold in the men's 3m Springboard.