While the outcome may have matched the first team's efforts later that afternoon, the scoreline was certainly different, with the Hammers taking a first half lead through Freddy Eastwood.
Leeds dominated second half proceedings, though, and fought back to take what appeared to be an unassailable lead.
However, with just two minutes remaining, McMahon struck to earn a point.
Academy Director Tony Carr said afterwards: "We played very well in the first half and could have been 3-0 up.
"To be fair, though, they dominated most of second half so we were pleased with a point after being 2-1 down until so late in the game.
"It was an encouraging performance against a very good team, run by Bryan 'Pop' Robson, who passed on his best wishes to everyone connected with West Ham."
Meanwhile, the under-17 side couldn't keep up the day's unbeaten record against our Yorkshire rivals, losing 4-2 against Leeds in a match also played at the Club's Chadwell Heath training headquarters.
Greg Pearson scored both the Hammers goals.
Under-19s team: Jackson, Metitiri, Dean, Johnson, Cleaver, Laurie, Allen, Cascione, Eastwood, Mehmet (Ritchie 50), D McMahon.
Under-17s team: Longstaff, Akinsete, Fletcher, Ward, Tattum, G.Carrick, Ferdinand, Saunders (Bunce), Pearson, Morris (Barrington).