Port Adelaide forward Willie Rioli will miss only one AFL game after having his two-game suspension for striking Collingwood defender Nathan Murphy halved.

Rioli's lawyer Ben Krupka was able to argue Rioli's slap on Murphy in the fourth quarter of Saturday night's Adelaide Oval blockbuster was low instead of medium impact.

The AFL Tribunal panel, however, stuck with the match review officer's grading of intentional conduct rather than careless as Port had hoped.

"The action used was more an open hand to the side of the head. There was only a small risk of injury," tribunal chair Renee Enbom said.

Rioli will miss only this week's Showdown against Adelaide and will be available for another crunch match the following round against Geelong at Kardinia Park.

Rioli pleaded guilty, but believed his strike was careless rather than intentional and said the impact was low instead of medium.

The only evidence Rioli provided himself was through a written statement, arguing he was trying to push away from Murphy and did not intend to strike the Magpies player.

"The contact was not hard at all. It was a push, the same as the push and shove between me and my opponent," Rioli wrote in his statement, read out by Krupka.

The lawyer argued Murphy was partly responsible for Rioli's contact being so high.

Murphy fell to the ground after the incident but was able to play out the thrilling game and suffered no lingering effects.

"Murphy's right arm is rising and there is some form of contact between the two arms," Krupka said.

"Murphy contributed to Rioli's arm going higher than intended. There is contact between Rioli's outstretched and the shoulder of Murphy."

Following the incident, Rioli was subject to vile racist abuse online.