Until further notice, Simeon is the king of Chicago.
The teams could meet twice more in the city and state playoffs.
“I really don't look at the rankings much, because once we're on the court, anything can happen,” Nunn said. “We definitely made a statement. We looked like a different team from when we started.”
Tate scored 12 points, including a driving layup on Okafor for the game's final two points with 30 seconds left, and Nunn had 10 points and six assists.
Parker had just seven points and six rebounds, but Simeon (18-2) held Okafor to eight points.
“Our guard play killed them,” Parker said. “Our bigs, we weren't there. But Jaylon and Kendrick, they really took it to them.”
L.J. Peak, a 6-foot-4 junior transfer from South Carolina, was outstanding for Young (18-2). He scored 14 of his game-high 20 points in the third quarter as the Dolphins turned a 13-point deficit into a 32-all tie after three.
All four of Simeon's Division I players made big plays down the stretch. Still, Simeon's lead was just 42-41 before Tate decided to attack rather than the pull the ball out and force Young to foul.
“Our coaches told us to be aggressive and try to get an easy basket,” Tate said. “We knew Jahlil didn't want to foul. I just wanted to be aggressive and make a play.”
Parker attacked a wide-open rim 13 seconds later, but his missed dunk left the door open for Young. Paul White missed badly on a 3-pointer, then Nunn blocked Ausar Madison's desperation heave at the buzzer.
Player of the game: L.J. Peak, Young, 20 points, 5 rebounds, 2 steals.
Key performers: Simeon — Jaylon Tate, 12 points, 3 assists; Kendrick Nunn, 10 points, 6 assists; Kendall Pollard, 8 points, 7 rebounds. Young — Jahlil Okafor, 8 points, 4 blocks; Paul White, 8 points, 6 rebounds.