United took the lead in the first half after a stunning solo run from Anthony Martial cutting in from the left saw Jesse Lingard presented with a chance he couldn't miss six yards from goal.
Lingard had earlier forced Keylor Navas into a fine save from distance and narrowly missed the target with a similar effort from outside the penalty area.
A strong Real side was replaced by a much younger one in the second half after 11 half-time substitutions, and it was the new talents keen on impressing that got Los Blancos back into the game.
Acting captain Casemiro fired home a clinical penalty after Victor Lindelof clumsily upended Theo Hernandez after the new Real left-back had burst forward at pace.
Marouane Fellaini later had social media in fits of laughter after badly miscuing a gilt-edged chance that came from a perfect cross from United talent Scott McTominay.
The ICC points were shared after the final whistle was blown at 1-1, but a penalty shootout followed to satisfy the American audience and determine which side would get a 'bonus point'.
And after a reasonable game, albeit one devoid of lots of chances, the quality disappeared.
You can only laugh at these penalties! From both sides. Absolutely awful! 😂— Hesham Bilal-Hafiz (@hesham786) July 23, 2017
After a strong performance in 90 minutes, Martial skied his opening penalty, while David de Gea in turn saved from Mateo Kovacic. McTominay, another who had performed admirably, then saw his effort turned away by Kiko Casilla, while De Gea saved again to deny Real youngster Oscar.
With no penalties converted after the first four, Henrikh Mkhitaryan casually stroked his effort into the bottom corner after a surprisingly anonymous 45 minutes from the Armenian, while Luismi Quezada also found the net for Real.
But Lindelof then failed to make amends for giving away the penalty in normal time and drilled a terrible effort straight down the middle at Casilla's legs. Hernandez, who had won that earlier penalty, also then missed.
United won 2-1, with both teams scoring just three out of 10 penalties between them.
"Yeah, three out of 10. But it's pre-season and to be honest, I didn't choose my best penalty-takers," was Jose Mourinho's comment afterwards.
Zinedine Zidane said, "I'm satisfied, the result isn't the most important thing, we gave a good account of ourselves. We finished well and we didn't pick up any knocks."