The Honda rider, who sealed the 2018 MotoGP title back in Motegi, outpaced the rest of the field by more than half a second in the rain-delayed wet-weather qualifying session.
However, after crashing on the bike he set his time on, Marquez returned to the track on his second bike in the closing minutes of qualifying and impeded Iannone at the hairpin-like Turn 9, compromising the Italian on corner entry.
Iannone was clearly unsighted by Marquez, who was looking the other way as the Italian passed and raised his hand to apologise to the incensed Suzuki rider once he noticed him.
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"I was going out from the box and just I let overtake [Andrea] Dovizioso and then I was in the hairpin and I looked behind, and I see only one Suzuki, that was [Alex] Rins, but because Iannone maybe was on the other side I didn't see him," Marquez said afterwards.
"So on the hairpin I was very tight inside but he overtook me from the inside [line].
"Of course maybe I disturbed him, if get penalised or not I don't know, race direction will decide, but you know I tried to avoid [impeding anyone], this is only what I can say, I didn't see.

Repsol Honda Team's Spanish rider Marc Marquez (R) is congratulated by Monster Yamaha Tech 3's French rider Johann Zarco (L) after scoring pole position during qualifying at the Phillip Island circuit on October 27, 2018, ahead of the MotoGP Australian Gr

Image credit: Getty Images

"Doesn't matter, I did the fastest lap, this is the most important for me."
Marquez had already been penalised for blocking a rival earlier this season, when he impeded Maverick Vinales in qualifying at COTA and was demoted from first on the grid to fourth - before going on to win the race anyway.
As a repeat offender, he has this time picked up a six-place grid penalty and will start seventh on Sunday.
Zarco, Valentino Rossi and Andrea Iannone will line up on the first row of the grid, with Andrea Dovizioso, Jack Miller and Danilo Petrucci forming an all-Ducati row two.
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