The Marylanders were called to battle before sunrise on August 27, 1776. Lord Stirling, the temporary commander of the Maryland troops, was awoken at around three o’clock in the morning and given the news that the British had begun their advance.  During the night, the British had surprised the American guard posted near the Red Lion Inn, and in the confusion, a number of Americans had been taken captive. General Israel Putnam ordered Stirling to take the two regiments “nearest at hand” and engage the British on the road near the Red Lion Inn.
Early in the morning on August 27, the alarm guns of the American lines sounded and the troops set to preparing the defense. Under General Putnam’s orders, Lord Stirling marched the First Maryland Regiment and Haslet’s Delaware battalion to meet the British. They were joined by Colonel Atlee’s Pennsylvania troops, Huntington’s Connecticut Continentals, and Kachlein’s Pennsylvania riflemen.
That morning the British were marching on the road to Gowanus without resistance. They were approaching Brooklyn lines until the Americans, under the command of Lord Stirling, blocked the British advance. Colonel Atlee’s Pennsylvania troops held off the British until the rest of the American troops had assembled upon the nearby ridge, which Stirling described as “very advantageous ground.”
On August 27, 1776, for the first time, the Americans met the British in a regular battle formation on the open field. An anonymous Pennsylvania soldier wrote that Stirling “immediately drew us up in a line, and offered them battle in the true English taste.”  The Maryland line held their position on the wooded Heights of Guana, firing down upon General Grant’s light troops, who were posted along hedges and in a nearby orchard, as well as General Leopold Von Heister’s Hessians. The armies also exchanged cannon fire from the hilltops that morning.
William McMillan was twenty one years old when he fought with Maryland troops at the Battle of Long Island. He and his brother, who were probably originally from Scotland, joined the First Maryland Regiment in December of 1775. For McMillan and the rest of the American troops, the battle that morning was fierce, but it was shaping into an American victory. Decades after the battle he would recall engaging in a “perty severe fight with yagers [Hessians]. It was a draw Battle, there was a good many on Each side killed. They retired and we did Not pursue them.”  The fighting continued until around midday, when the British pulled back.
That morning it seemed that the inexperienced, ill-equipped, outnumbered American army had fought off one of the world’s premiere military forces. The feeble attack mounted by the British emboldened the American troops, who were testing themselves for the first time on the battlefield. According to the anonymous Pennsylvanian who was present at the battle, “our men stood it amazingly well; not even one of them showed a disposition to shrink.” The Pennsylvanian continued, “when they [the British] perceived we stood their fire so coolly and resolutely, they declined coming any nearer, although treble our number.” The retreat of the British galvanized the Americans, who, he wrote, “cried out, the day is our own.” 
However, the day was not yet won. The force the Americans faced that morning served as a noisy diversion, and 10,000 British troops to the rear of the Americans were laying in wait for the signal to attack.
 Henry P. Johnston, The Campaign of 1776 Around New York and Brooklyn, New York: Da Capo Press, 1971, 163
 Pension of William McMillan, The National Archives, (Revolutionary War Pension and Bounty-Land Warrant Application Files), NARA M804, S 2806, 33. From Fold3.com.