He made a driving layup, was fouled, and sank the free throw.
"Everybody's going to remember those last couple of plays, but that's what great players do," Neumann-Goretti coach Carl Arrigale said.
Imhotep had two free throws for a chance to tie it with 18.2 seconds remaining, but made just one.
Newton, who sealed it with two free throws with 8.3 left, finished with 22 points and was named the game's MVP.
"Past teams never got the chance to do this," Newton said of playing for a city title, "so I'm just making up for what they didn't get to do. So I came out here and won it for my team."
Imhotep's loss came despite the efforts of Providence-recruit Brandon Austin, who scored nine of his 18 points in the fourth.
Since a stinging, 17-point loss to Chester in a nationally televised game, Neumann-Goretti has been on quite the roll.
"After that game," Newton said, "we knew we had to self-check. We had to play as a team. We had to get better every day. We just went in the gym and worked."
Neumann-Goretti has won three straight Class AAA state titles and five straight District 12 crowns. Imhotep has won three of the last four Class AA state titles.
But only one could call itself city champion.
Neumann-Goretti 10 14 15 13 – 52
Imhotep Charter 11 9 9 22 – 51
N-G: Tony Toplyn 2, Troy Harper 6, Lamarr Kimble 10, John Davis 7, Jamal Custis 5, Ja'Quan Newton 22.
IC: Brandon Austin 18, Abraham Massaley 2, Nigel Grant 11, Jakwan Jones 2, Deion Evans 2, Deryl Bagwell 11, Jalil Myers 2, Basil Thompson 3.
Contact Tim McManus at firstname.lastname@example.org. Follow on Twitter @ByTimMcManus.