Cook pasta al dente, following instruction on the package.
Heat olive oil in the frying pan, fry onion, chili and garlic about 3 minutes, add tomatoes. Sprinkle with sugar, pepper and salt. Cook till sauce thickens.
Add pasta mix well.
Pour 6 tablespoons of water in separate pot, put in clams, simmer till they open about 4 minutes. Drain on sieve, remove closed clams.
Transfer open clams to the frying pan and mix with pasta.