He volleyed home a long cross from Javier "Chicharito" Hernandez in the 55th minute, timing his run perfectly to knock the ball into the far side of the net — then leaping and punching the air.
Moments later, Luke Shaw found Mata at the top of the penalty box, and Mata's quick blast deflected past Simon Mingolet for a 2-1 lead. After Lingard added the insurance goal, Rooney stood still for a few moments, his arms outstretched in celebration.
Both teams substituted liberally in the second half.
"Overall, I'm delighted with the whole tournament," said Liverpool manager Brendan Rodgers, who came away confident that his club will be ready for the start of Premier League play in about two weeks. "We worked very, very hard."
The scoring opened in the 14th minute, on a play that Manchester United argued to no avail.
Liverpool's Raheem Sterling chased down a ball on the left side of the box near the goal line, as Manchester United's Phil Jones scurried over to defend. Jones went for a slide tackle and while replays showed he appeared to make contact with the ball, the play also sent Sterling to the grass — and referee Mark Geiger immediately signaled for a penalty kick
Gerrard went one way, Manchester United goalkeeper David De Gea guessed the other, and Liverpool had a 1-0 lead.
It's the second straight year the tournament concluded with a high-profile title match in South Florida, which has a strong and diverse soccer following. That's among the reasons why David Beckham, one of the sport's biggest stars, has been trying to get a stadium built in downtown Miami for an expansion MLS franchise.
Real Madrid topped Chelsea in last year's final.