The Adelaide forward will need surgery after he suffered a depressed cheekbone fracture in the incident, which happened during the frenetic last quarter of Sydney's controversial one-point win.
The Swans successfully argued the collision was an accident, caused by McCartin having to change direction as he was chasing the ball.
McCartin was facing suspension for Sydney's home game on Sunday against Melbourne and then their elimination final, meaning the ban could have ended his season.
"Although when viewed from certain angles this action looks like a bump, we heard McCartin's explanation and looked at the footage and the stills showing all angles, we are not satisfied it was a bump," the tribunal said in its ruling.
"We find ... that the way in which McCartin responded to a late and sharp change in direction of the ball was not unreasonable.
"There was little else he could reasonably do than himself change direction, decelerate and ride the inevitable impact, which he did."
Also on Tuesday night, the Western Bulldogs unsuccessfully challenged defender Taylor Duryea's one-game rough conduct ban for his bump on West Coast forward Jamie Cripps.
It means Duryea will miss the Bulldogs' must-win game against Geelong on Saturday night at GMHBA Stadium.
They must also rely on Carlton beating GWS to make the finals.
The tribunal found Duryea bumped Cripps so he could gain possession and that the contact was forceful.
"Although Cripps was not injured, he suffered a forceful high blow and was knocked off his feet. The potential for a concussion or facial injury was not insignificant given that he was exposed and Duryea was coming at speed," it added.
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