The Battle of Borleias started when Lord Vexen led a Sith fleet of three capital ships and eight frigates along with 25,000 troops against the Galactic Alliance garrison force of five frigates and 10,000 troops. Most of these ships and troops were from the Nymean Ascendancy and wanted revenge for the previous Galactic Alliance attack on Areltsi.
With Lord Vexen was Lord Synyster, Zathri, and Lord Boran. These four managed to rout the initial garrison fleet and land on the planet with their army. For the first day, fighting goes well for the Sith. Vexen managed to duel and kill Jedi Master Dix-Rut and crush the initial Galactic Alliance forces.
However, early on the second day, a large Galactic Alliance fleet of four capital ships and ten frigates emerged from hyperspace on the Sith fleet's flank. This force, led by Grand Master Vos crushed the Sith fleet and drove them from orbit. With the Sith fleet out of the fight, he was able to land an additional 50,000 troops.
Once on the planet, Vos tracked down and confronted Vexen. He offered a surrender to end the fighting, but before a decision could be made, Synyster and Zathri joined the confrontation. Synyster trapped the group inside a damaged hangar and intended on killing Vos. Boran choose this moment to blow open a hole in the rubble and join the fight. Despite their numbers, Vos managed to separate them and defeat them individually. Vexen lost an arm but managed to escape. Synyster and Zathri were defeated and captured. Seeing the others fall, Boran joined Vexen in retreating from the battle.
The Sith lost heavily in this battle and it was a resounding victory for the Jedi. Due to the losses suffered here, the Nymean Ascendancy was forced to withdraw from active combat in order to protect its own borders.