The appeal of two of the world's most iconic sports teams attracted fans to the International Champions Cup match at the University of Michigan's American football stadium in Ann Arbor.
The previous U.S. record attendance for a soccer match was 101,799 at the 1984 Olympic final between France and Brazil at the Rose Bowl in California.
The largest crowd ever to watch a soccer match was at the 1950 World Cup in Rio de Janeiro when 173,850 paying spectators came to the Maracana for the Brazil-Uruguay final clash, though unofficial estimates put the attendance as high as 210,000.
Two first-half goals by Ashley Young proved enough to help United beat the European champions on Saturday despite Real's world record signing Gareth Bale scoring from the penalty spot.
United's win means they advance to Monday's final in Miami, where they will meet traditional English rivals Liverpool.
The crowd got an added bonus when Cristiano Ronaldo made a surprise appearance for Madrid in place of Alvaro Arbeloa in the 74th minute, having been ruled out of contention before the match with what was reported to be an injured left knee.
Young had opened the scoring in the 21st minute when he capped off a 20-pass move to beat keeper Iker Casillas at his near post from about 12 metres.
Real equalised in the 27th when Bale was fouled in the box by United defender Michael Keane and then got up to convert the penalty by sending David De Gea the wrong way.
However, it took United only 10 minutes to regain the lead when Young curled in what looked like a cross from the left. United's England forward Wayne Rooney timed his run perfectly but did not appear to make contact with his attempted header.
His presence distracted Casillas, though, with the keeper reacting too late to stop the ball curling inside the far post.
United, playing under new manager Louis van Gaal, padded their lead in the 80th when substitute Javier Hernandez headed home an exquisite pass by Shinji Kagawa from close range.
"I think we were fantastic from the first minute to the end," Young told Fox Sports.