The night started badly as Christian Pulisic curled home from range to put the hosts ahead.
But Germany had been the better side and a routine tap-in by Ilkay Gundogan drew them level in Connecticut.
Nagelsmann's side were much improved in the second half and Niclas Fullkrug and Jamal Musiala scored to seal a comfortable victory.
After Hansi Flick was sacked in September following a poor run of results, culminating in a 4-1 defeat by Japan.
Exempt from European Championship qualifying, Germany continue the Nagelsmann era in a friendly with Mexico on Tuesday evening (Wednesday 01:00 BST) in Philadelphia.
Access our platform effortlessly on-the-go through our user-friendly mobile apps.
𝗦𝗲𝗺𝗮𝘀𝗼𝗰𝗶𝗮𝗹 𝗶𝘀 𝘄𝗵𝗲𝗿𝗲 𝗿𝗲𝗮𝗹 𝗽𝗲𝗼𝗽𝗹𝗲 𝗰𝗼𝗻𝗻𝗲𝗰𝘁, 𝗴𝗿𝗼𝘄, 𝗮𝗻𝗱 𝗯𝗲𝗹𝗼𝗻𝗴. We’re more than just a social platform — from jobs and blogs to events and daily chats, we bring people and ideas together in one simple, meaningful space.
