Scheffler and Koepka looked to have held the upper hand on the 18th green with their 1up lead, only Rahm had other ideas as he drained his eagle putt from 30 feet to win the final hole and tie up the match.
It marked the second eagle on the last three holes for Rahm, who chipped in on the short par-4 16th before going absolutely bonkers.
Europe ended day one with a healthy 6.5-1.5 lead to take into the weekend at Marco Simone Golf Club in Rome, Italy.
No doubt frustrated with how the first day panned out for Team USA, Koepka, who was benched in the morning foursomes session, slammed the attitude of Rahm when speaking to the media after their fourballs match.
Koepka was asked how he was feeling after the round, to which he sounded out Rahm:
Koepka is expected to play a large part in proceedings on Saturday having been benched for the opening session, much to the surprise of American golf fans.
The opening day of the 2023 Ryder Cup marked the first time Team USA failed to win a single match.
The team that has led the Ryder Cup after day one has gone on to win 70% of the time.
Team USA also have not won a Ryder Cup on European soil since 1993.