McMahon went 1-for-2 with a double, two walks and a run scored in Friday's 6-1 win over the Marlins.
The 24-year-old is off to a quick start at the plate as he attempts to seize control of the starting second base job for the Rockies, getting on base in half his plate appearances through two games, Garrett Hampson will probably be heard from sooner or later, but if McMahon can go on a tear early, he could end the competition before it's really begun.