Sun and his long-time rival Park Tae-hwan shared silver medals at men's 200m freestyle final at London Aquatic Center, while French superstar Yannick Agnel bagged his second gold after a team relay victory in the previous day.
South Korea's Park Tae-hwan (L) shakes hands with China's Sun Yang after both won silver for the men's 200m freestyle final at the London 2012 Olympic Games at the Aquatics Center, July 30, 2012.
In the dramatic race, Agnel was already in the lead by the time he surfaced following his initial dive off the starting block. Sun had a sluggish reaction time and was sixth after the first 50m.
Later Sun roared on and chased closely US Olympic champion Ryan Lochte and Park who were second and third placed after 150m.
The last 50m changed everything. Sun put on a devastating burst and dropped Lochte behind to finish the second together with Park.
Agnel took the gold with a sizzling 1:43.14, nearly two seconds faster than runner-ups Sun and Park, who tied in 1:44.93.
Sun, earlier said he did not expect a medal in the final for this was his weakest event, was extremely excited with the result. He chatted with Park before stepping on the podium together, flashing giants grins for photographers.
Sun threw the bouquet to his parents who cheered for him on the audience tribune together with a capacity of Chinese fans.
"I never expected such a dramatic finish with two swimmers taking silver medals in the same race," said Sun.
"But it is good for me and for Park," he said. Park lost to him to pocket a silver in the 400m freestyle final two days before.
"I didn't expect to win silver in this event as it is not my best. I would have been happy with a bronze medal," said Sun, who is dominant in long distance and is tipped as the overwhelming favorite in the 1500m freestyle.
Sun had an emphatic victory in men's 400m freestyle two days ago over Park, who Sun has been chasing for several years. This time, they tied, but satisfactory for both.
Park, who seemed yet to recover from the sorrow of losing to Sun two days before, said he didn't have confidence before the race.
"My teammates encouraged me and they said I had trained really well, so do your best," said the 22-year-old, silver medalist of the event at Beijing Games.
"I didn't get gold but because my competitors were such high-ranking athletes. It was an honor to be with them in the same race," he added.
Agnel, who turned over Lochte in the last leg of men's 4X100m freestyle relay a day before to give France a team gold, now had another victory in the 200m freestyle over Lochte, who was winner of the event at the Shanghai World Championships last year.
He said he did not expect Lochte and other competitors to be so slow. "It (gold) is above all my hopes and expectations, especially the time I did," he said.
"I started really quickly on the first 100 metres because I knew I was the fastest," said the 20-year-old, currently ranked world No 1 in 200m freestyle.
"I tried to retain my speed with a little sprint over the last 50. I'm really happy it worked," he added.
China's Sun Yang poses with his silver medal for the men's 200m freestyle final at the London 2012 Olympic Games at the Aquatics Center, July 30, 2012.
It is the first Olympic medal China had ever won in 200m freestyle, though Sun said he still felt sharp gap in catching up with Agnel's mark.
It also marks Sun's second Olympic medal in London, following his gold in the 400m freestyle that made him the first Chinese male Olympic champion.
Since smashing Australian distance swimmer Grand Hackett's decade-old 1500m world record at Shanghai World Championships last year, the Zhejiang native had become the vanguard of China's growing supremacy in pool.
The 20-year-old, under the tutelage of Hackett's former coach, had a clutch of world best times this year.
France's Yannick Agnel waves after winning the men's 200m freestyle final during the London 2012 Olympic Games at the Aquatics Center, July 30, 2012.
One gold and one silver so far in two of his three events was more than happy for Sun, as the rest 1500m freestyle is his signature event. Another gold, or at least a medal beckons for him in the 1500m freestyle which falls on the last day of pool events on Aug 4.
Lochte, who upset Michael Phelps to win men's 400m individual medley on the opening day, fell out of the podium as fourth.
Paul Biedermann, who is defending Olympic champion of 200m freestyle and tipped as the top seed, only settled for a fifth place.