Yes, absolutely - though not in the way you might think!

The US came into the war just as Russia was knocked out of it and the Germany high command realised that with the massive manpower and manufacturing base of the US, it was only a matter of time before the war was lost. It was therefore imperative to try and win the war before the Americans arrived en masse - there would be over 300,000 US soldiers in France by May 1918 and a further million by August.

Forces were redeployed from Russia as fast as they could and a massive offensive - Operation Michael - was launched in March 1918. The German spring offensive broke through the British lines on the Somme and succeeded (finally!) in breaking the trench deadlock and getting through into open country, thanks to tactics learned on the eastern front - a short "hurricane bombardment" instead of days of shelling, and infiltration and stormtrooper tactics.

With the British forces reeling back and the French fighting on the flanks, it looked for a while as if the Germans might actually manage to take Paris, and Haig issued a general order that all British forces were to stand firm, backs to the wall.

Unfortunately for the Germans, the offensive petered out short of Paris thanks to a combination of dogged British defence and French attacks along the flanks of the German line; the difficulties the Germans found in advancing over the shell-ravaged Somme battlefields from two years earlier and the tendency of German troops to drop everything and start looting whenever they took a British supply dump.

Once the German offensive ground to a halt in August, the Allies counter-attacked, pushing the Germans back to the old trench line and then beyond it, in the "Hundred Days Offensive" which continued until the Armistice in 1918. These last 9 months of war were a far cry from the trench warfare that is the usual image of WWI and actually it wasn't until the Hundred Days that US forces were engaged in any number, so the American experiences of WWI were in general somewhat different from those of the British and French, with Pershing's American Expeditionary Force deployed along the Ardennes region in the French sector and attacking along the Verdun-Sedan axis.

So in WWI the American troops played a significant part in winning the war without actually doing a huge amount of the fighting. If the war had gone on another six months or so in the trench warfare phase, we'd have seen huge American armies manning the trenches and probably having their own Sommes and Verduns while they learned the lessons of Trench Warfare, but as it was it was the mere threat of the American arrival that forced the Germans to risk it all on an all-or-nothing attack.