First Battle of Ord Biniir

The First Battle of Ord Biniir took place several weeks before the Battle of Yavin. A group of Rebel Y-wings defeated the 223rd Imperial Fighter Group which guarded the planet Ord Biniir, thus paving the way for the Rebel capture of the planet.

Behind the Scenes
This is presumably the first Rebel victory mentioning in the opening crawl of A New Hope.