In the harbor, the best way to defeat Sergio is to first kill the four gangsters in the start of the mission and immediately get in your car again. Use the car as a shield and run over every other gangster you see. Do not worry about the snipers; the car will protect you from their shots. Move to the warehouse that Sergio is hiding in (with the Sergio's green car outside it) and continue forward. There will be another large building after it and behind that building there is another gate. Get out of the car and check its window's very carefully. There is a sniper standing in one of them. Wait until he turns around, then shoot him. Take his rifle and continue.
In this chapter you have to find Sergio Morello and kill him. Kill the four guards at the beginning, then kill the other three guards. They will arrive in a truck. After that, get into your car and drive it through the left side of the port (where there are grassy fields). At first, two guards will jump in your car then you will see a house at the end of the port. In front of that are two men standing with pump action shotguns. Kill them. You will see another house beside the previous house. Get out of your car go into the house. Search it. You will see a man standing in front of a window with a sniper rifle in his hand. Kill him and take his weapon. You will also find a medical kit in that building. Get out of that building and kill the other four snipers. Then, move to the warehouse that Sergio is hiding in (with his green car outside). You will find that all the gates are locked. You must break a door. You will see a railway track heading to the large gate. You must break the gate by colliding into it with a train. At the corner of the port, there are two oil tankers on the railway track. Join the railway lines with the switch (with the big handle). The tankers will start rolling and collide with the gate. You must roll the tanker. There is a small piece of wood placed near the front wheel of the first tanker. Remove it and watch what happens. Note: You will find grenades at the railway station and a medical kit in the railway building. There is another medical kit in one of the dispatch halls. After you explode the oil tankers, go towards the warehouse. You will see someone shooting at you. Kill him, then wait. Two men with shotguns will come from the left side of the warehouse. Kill them. There will now be a man with a shotgun on the right side of the warehouse. Kill him. If you go in deeper you will see another man with a shotgun. Take him out. At the very back of the warehouse is Sergio. Be careful; he has a Thompson. Wait until he turns around, then shoot him. Return to the metal boxes quickly as he turns to face you. Once again, when he turns around get out and then kill him. Get his Thompson then get out of the warehouse. Get the truck and run over the people that are shooting on your way out. Once you get out the way you entered, just return to Salieri's bar.