I'm working on something with an earlier ARW victory for the US that involves this, I think along with a better showing at Brandywine would be better.
However, one of the keys would be no fog - on a different day the Americans would have a clearer picture of enemy forces. I don't know if you can get a decisive victory, but you can get the type where the British are forced to march through heavily rebel New Jersey and get blasted by farmers hiding behind haystacks, farmhouses, etc..
Hmm... A victory here or at Brandywine would have massive implications.
Howe literally abandoned the Northern campaign in order to take Philadelphia, which led to the Battle of Saratoga. It was a major loss of face for Howe OTL even though he captured Philly. If Howe fails to capture the city then this and Saratoga could be the one-two blow to British morale that could end the war.