Elrond fled with the other Elves of Eregion to the Valley on the North of the Misty Mountains. Sauron, in the beginning, paid little heed becuase he suspected that Gil-galad, being the High King of the Noldor and thus Celebrimbor's superior, was in possession of all three Elven rings, although in truth he had two. Because of this, Sauron was focused on defeating his ancient enemy and this spared the survivors of Eregion from annihilation. But knowing that Elrond will attack him from the rear, he sent a small force to lay seige on Rivendell. This force was eventually defeated just in time for Elrond to come in from behind, crushing Sauron's forces that survived the Battle of Gwathlo between his army and that of Gil-galad and the Numenoreans.