Sulla's initial goal was the immediate conquest of Mithridates' strongholds in Greece. Athens and its main port, the Piraeus, were the obvious targets and Sulla ordered a direct assault. Defended by Archelaus, the plan was nearly a disaster as the walled port was in excellent defensive position with access to reinforcement by sea. Sulla was forced to withdraw in order to secure local funding and prepare proper siege equipment. The entire campaign year of 87 BC was spent in siege of both Athens and Piraeus with little success. By the winter, Sulla abandoned his plan on the Piraeus while keeping the siege of Athens intact. A chief legate, Lucullus was sent abroad to Egypt and Syria in order to arrange for a fleet, with the hopes that naval operations could stave off re-supply and reinforcement.
By Spring of 86 BC, however, the tide turned for Sulla, despite the absence of Lucullus and his fleet. Athens finally surrendered and the town was sacked. The assault on the Piraeus was continued but Archelaus sensed the situation to be untenable and finally decided to withdraw. The Piraeus was burned upon its capture, but without a fleet to block access to the sea, Archelaus' army was able to get away unharmed. He continued on to Macedonia, where a new Mithridatic army had recently invaded and taken control from the Romans. Archelaus joined with and assumed command of this newer force nearly tripling the size of Sulla's manpower. With renewed confidence Archelaus moved south once again into Greece to face Sulla.
The two armies would meet at the town of Chaeronea in Boeotia. Marching south from Thessaly, Archelaus an able commander, positioned himself on high ground and in a position to cut off Sulla's route of supply and escape. Sulla was forced to give battle in a greatly outnumbered situation. Under a full assault, Sulla's veterans managed to hold under the pressure. Sulla proved his military brilliance by personally ordering the movement of troops to key positions throughout the battle. Shoring up weakening lines and exploiting advantages left by the enemy, the Romans managed to persevere. Eventually, Archelaus' own flank broke and what seemed to initially be an excellent opportunity for him, turned into a full scale rout of his army. He managed to escape with about 10,000 men, but his losses were far greater. Hailed as imperator by his men (a requirement for a triumph) Sulla was left at least temporarily in complete control of Greece.
With his rival, Cinna, taking control of Rome and all the ensuing political upheaval, an additional Roman army under Flaccus was sent to occupy Mithridates in Asia. Since Sulla had been earlier declared a public enemy to Rome due to his actions in marching on the city before his eastern campaign, Sulla was concerned over this new army's real destination. As it marched through Macedonia to meet with with an apparant objective to counter Mithridates, Sulla moved north to keep an eye on it. Archelaus, meanwhile, was given time to gather strength and recruit a new army on the island of Euboea. Flaccus apparently had no intention of interfering with Sulla, but in the interim Archelaus crossed back into Boeotia, forcing Sulla moved to move south. Meeting at the town of Orchomenos Sulla's forces began to dig in defensively, but with little time to spare before Archelaus' arrival, they were unable to complete their preparations. In another hard fought battle, the Romans again defeated Archelaus. This time though, the encounter was a complete victory and Greece was completely at the whim of Sulla. Mithridates had already lost 2 large forces in Greece, faced impending invasion by Flaccus and was now also in the precarious position of putting down unrest in his recently conquered Asia. Despite their actions against the Roman citizenry there, the local towns were seemingly beginning to realize that they had made a huge mistake and hoped that rebellion against Mithridates would win them leniency for their actions in the earlier mass killing of Roman citizens and allies.