McMahon, called "the Green Mountain Boy" continued wrestling throughout the United States and Canada and went undefeated until 1878. On July 22,1873 in Troy, N.Y. McMahon met Thomas Copeland of Montreal. The match was billed for the championship of the U.S. and Canada. McMahon was strongly favored and there was little betting despite the heavy odds being offered. Another collar-and -elbow wrestler named Homer Lane served as the referee. Copeland won the initial fall in six minutes, only to lose the next two in a little less than a quarter of an hour. McMahon completely out-classed his opponent
and it was suspected that he let Copeland take the opening fall.
The following month at Harry Hill's Coliseum in New York City McMahon was matched with Albert Ellis, "the champion wrestler of England ". The venue was packed with fans, many having made the trek from Boston, Chicago, Baltimore and Philadelphia. Ellis weighed in at 138 pounds, compared to McMahon's 192 lbs.
Due to the weight difference the match was held under Devonshire and Cornwall rules, similar to collar-and elbow but requiring the use of a jacket.
Homer Lane was selected to be the referee. It was noted that Ellis was well conditioned, while the Green Mountain Boy appeared "soft and flabby". Though Ellis demonstrated greater agility and technical know-how, he could not overcome McMahon's superior size and strength. McMahon won the opening fall with
a powerful cross buttock. 
Ellis' corner disputed the fall and the match was nearly broken up over the ensuing controversy. Ellis gamely consented to continue and allow his opponent the fall. The Englishman was given the second fall on a foul. Going for the winning fall Ellis cleverly avoided several falls, when upon being thrown by McMahon he swiftly reversed himself before hitting the ground and landed face down. The fans heartily cheered his displays of dexterity. McMahon finally managed to slam Ellis flat on his back, thus winning the contest. A newspaper account reports, " A Great deal of money changed hands on the event."
Exactly a year later, again at Harry Hill's, McMahon and Ellis met for a rematch. Ellis had stayed in America wrestling exhibitions and working as a stonemason.
Each man put up $500 and the match was again under the jacket rules. It was further stipulated that choking and kicking above the knees was barred. Harry Hill was the third man in the ring. McMahon tried over and over again to throw the diminutive wrestler but was out-foxed by his technique. McMahon used an inside leg lock and sent Ellis earth-bound, only to have the Englishman turn and land on his hips. Tired and angry, the American shouted, "If that wasn't a fall, I will leave", whereupon he jumped out of the ring. Hill gave the wrestlers a five-minute rest and stated that if only one man returned to the ring he would be awarded the entire stake. McMahon composed himself and returned to the ring. Hill discussed the match with both wrestlers and than declared the bout a draw. Yet a third match was held, this time for $700 a side. McMahon won.