The Battle of Harlem Heights took place on September 16, 1776, shortly after the Continental Army's defeat at the Battle of Long Island.  Washington's forces, though initially surprised by the British advance, rallied and successfully ambushed the British troops, ultimately forcing them to retreat. This victory, the first for the army under Washington's direct command,  boosted morale and provided a much-needed respite for the struggling Continental Army. 

Thanks to Wikipedia and Google Gemini for providing the details to help craft this story.