Pentathlus' Expedition to Sicily of c.580 was probably one of the first clashes between the Greeks and the Phoenician inhabitants of western Sicily, and ended with a victory for the Phoenicians and their local allies.
During the previous two centuries the Greeks had slowly been spreading west across Sicily, but their colonies hadn't directly threatened the three main Phoenician cities of Motya, Panormus and Soluntum, on the western and north-western coasts. The Greeks had founded a city at Selinus, on the south-west coast, but their main opponents appear to have been the Elymians, one of the three native groups on Sicily.
This changed in around c.580, when an expedition of Greeks from Rhodes and from Cnidus, on the south-west coast of Anatolia, decided to found a new city on Sicily in an attempt to escape harsh treatment by the kings of Asia. Diodorus Siculus dates this expedition to the Fiftieth Olympiad (580-576 BC). The colonists chose Penthalus of Cnidus, who claimed descent from Heracles, as their leader.
The new city was founded at Lilybaeum, on the west coast of Sicily and located just to the south of the Phoenician settlement at Motya. If it had been successful, the new colony would have been a direct threat to Motya's prosperity. There are two accounts of the destruction of this colony. According to Pausanias the colonists were defeated by an alliance of Elymians and the Phoenicians of Motya.
Diodorus gives a more detailed account of events. When the colonists arrived they found the Greeks of Selinus at war with the inland Elymian city of Segesta (or Egesta). The colonists decided to aid Selinus, but the allies suffered what must have been a heavy defeat in battle. Penthalus was killed and the survivors decided to abandon the new colony and return home. Although the Phoenicians aren't mentioned here, there is no reason to believe that they couldn't have fought alongside their Elymian allies, reconciling the two accounts.
This wasn't the end of their story. On the way home they stopped at Aeolian Islands, off the north coast of Sicily. They decided to settle on the islands instead of returning home. They were apparently welcomed by the inhabitants of the island of Lipara, the survivors of an earlier Greek colony, and there established a successful society (at least partly based on piracy).