Westhoff was charged with striking Essendon's Cale Hooker in the third quarter of last Sunday's clash at Etihad Stadium, drawing 225 demerit points and a two-game sanction.
His six-year good record reduced the penalty to 168.75 demerit points, however, and a one-game ban, giving the Power a free swing at the Tribunal.
The right-arm blow to Hooker's chin was assessed as intentional conduct, low impact and high contact.
Westhoff argued that his conduct was reckless and not intentional, but the jury of Emmett Dunne, Wayne Henwood and Wayne Schimmelbusch took just four minutes to disagree, upholding the one-week ban.
Westhoff told the Tribunal that Hooker made a beeline towards him at the end of the third quarter so he used his right forearm, intending to strike the Bombers’ defender across the chest.
"There was going to be some sort of confrontation, neither of us was going to back down," Westhoff said.
"He came at me with some kind of force and I didn't want to back down from that. That's the way AFL is played.
"I didn't want to show any weakness."
Westhoff's case appeared futile from the beginning when chairman David Jones outlined that if the forward was found to have intentionally struck Hooker – to any part of his body – the intentional charge would be upheld.
Westhoff's counsel, Mark Griffin QC, made the case that Westhoff intended to strike Hooker to the chest, but his forearm slid up to make contact high.
Umpire Chris Kamolins, who reported Westhoff on the spot, gave evidence and said Hooker had told him at the start of the fourth quarter there was nothing in the incident.
A medical report from Essendon showed no damage had been done to Hooker.
Westhoff has kicked 20 goals and averaged 18 disposals in a strong season for the Power.
Young forward John Butcher shapes as a likely replacement for the reinvigorated goalkicker this week.
Nathan Schmook is a reporter for AFL Media. Follow him on Twitter @AFL_Nathan
