Nicholas Tse did not receive an Oscar nomination for portraying Deng "Si" Sidi in Bodyguards and Assassins.
Nicholas Tse plays one of the followers of Sun who drives a rickshaw and seems to be friends with pretty much everyone. Si is a relatively simple part in the first half as Si is just a lighter part there for a little comic relief and pleasantness among all the fighting and death. Well Tse certainly fulfills this duty as he is incredibly endearing in every scene he is in. He just has this warmth and energy in these scenes that he makes Si quite likable. Tse very skillfully plays the part making sure that Si never becomes precocious, but rather just earns Si's whole bright demeanor. His screen time is relatively scattered but he does a good job of making himself known whenever he is on screen with his enjoyable presence that does well to make the proceedings seem a bit less bleak.
The second half of the film basically is when every bodyguard takes their turn protecting the decoy Sun used to distract the assassins. In turn each of the bodyguards get their own very dramatic death scene as they sacrifice themselves for the greater good. Si is not exactly a bodyguard really rather he is just driving the rickshaw that the fake Sun is hiding in. For most of the journey though Tse is very moving in his portrayal of Si's reactions to the deaths of his compatriots as well as seeing one of his friends taking up the dangerous job as the fake Sun. Tse role is still relatively simple but he makes the most of basically every quick reaction shot he is allowed, bringing a great deal poignancy to each moment of the gauntlet.
Eventually the numbers are thinned to such an extent that Si himself must attempt to stop the head assassin even though he is obviously not a fighter, and certainly is no match for the man. All Si really can do is grab the man's leg in his futile attempt to stop him and Tse makes the scene very affecting because of how much passion he puts in the moment, and Si's sacrifice is truly felt. It only makes it more heartbreaking because of how much he made you care about Si before this point. This is a fairly simple performance and because of the large ensemble nature of the film his screen time is brief. Tse more than fulfills the needs of the part though and even with those limitations he manages to give a good performance that manages to be one of the most memorable aspects of the film.