On Tuesday's first half of the two-night finale show, the acts demonstrated their talent one last time.
Monsters and Critics' money is on Courtney Hadwin to take the top spot.
Courtney, from Hesleden, Co Durham, failed to take home the £760,000 prize after finishing in sixth place on the smash hit show.
When Ketterer came out during the final night of performances on Tuesday, he delivered a raw, emotional rendition of the soul classic, "Ain't No Mountain High Enough".
"We always believed she would do well in the USA". Michael Ketterer stood out not only because of his voice but also for being a pediatric nurse and father of six kids. Even the runners up, dance troupe Zurcaroh, were thrilled for him, immediately surrounding him and lifting him into the air upon his win.
Those vying for the ultimate title were Shin Lim, a magician who has stunned audiences with his close-up magic; Michael Ketterer, a pediatric mental health nurse who brought Simon Cowell to tears; Zurcaroh, an Austrian aerial dance group who quickly became Tyra Banks' choice for a victor; Duo Transcend, married aerialists who never shied away from a risk; Samuel J. Comroe, a comedian who has embraced his Tourettes Syndrome as part of his act; and Daniel Emmet, an opera singer with a penchant for picking nontraditional songs.
Cowell and the other judges encouraged him to step up his game and add new tricks each week, and Lim bravely accepted the challenge with a final act that also featured his piano skills.
Following the performance, judge Howie Mandel said: "You are on fire, you're fantastic. You've got to show your personality, you've got to be a showman".
"I felt a reaction in the room tonight when he sang the Garth song, it was actually incredible, and yeah, we are going to be working together, there's no doubt", Cowell said.
He walks away with a cool $1 million and will headline his own show at the Paris Las Vegas Hotel in November.
Cowell previously said that Garth Brooks should write for the contestant.