To me, this matchup really isn't debatable. As soon as Kakuzu starts pressurizing Itachi with the Elemental blast combination, Itachi would pull up the Susanoo, rendering any and all attacks useless against him, as stated in the Databook [
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] I've also seen the underground thread argument before, but just like PDG said, Itachi's Sharingan allows him to see chakra, even when underground [
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] Whether the threads would manage to get through even without this ability is debatable, since the Yata Mirror has been shown to be able to change it's size and shape [
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], meaning that it could probably also protect from attacks from underneath. After all, it was said to be able to change
every one of it's properties.
After Itachi decides to draw out the Susanoo, the slim chance Kakuzu had of winning gets close to zero. He doesn't have the speed to handle the Amaterasu or the wide ranged attacks of the Susanoo, and in the meanwhile, can't harm Itachi at all.
To be honest, whether Itachi will need to use the MS techniques is debatable. Just like Itachi isn't used to bringing out the MS techs early in a fight, Kakuzu has been shown to start out fights by using close combat to draw the enemy near, and using a combination of the Earth Grudge Fear and the Doton Domu to bring down the opponent, which would provide some difficulties against a Sharingan user. The reflexes granted by the Sharingan are truly something to be reckoned with, and it's ability to see chakra, along with the boosted eyesight would allow Itachi to react in time to the threads, allowing him to retreat to a safe place.
A way to get through the Doton Domu would for example be to use Clone Feints. In order to completely harden his skin, he needs to use a hand seal, which of course, requires some time. A possibility for Itachi would be to use the same strategy he did against Kakashi, and switch out for a clone (As we've seen he had enough speed to do that without even Sharingan noticing [
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]), and wait for Kakuzu to come up close, just like against Kakashi and Kurenai [
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-
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] Kakuzu, seeing as he wouldn't even be aware of the clone, would attack without hesitating, which would severely damage him, as he wouldn't have the time to form the hand seal.
There's also, of course, the danger of Itachi catching him in a Genjutsu. In a close up fight, Itachi has been shown to be able to catch guys like Killer Bee in a genjutsu without him noticing [
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] His proficiency was great enough for him to even be able to lay a Genjutsu on people with a single finger [
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] Of course, there's always the argument that Kakuzu's masks might be able to snap him out of it, but even so, the time it takes for that to happen would give Itachi an opening to catch him in the Tsukuyomi, something the masks wouldn't be able to snap him out of.
All in all, Kakuzu has close to no chance. The only threat in his arsenal would be the elemental blasts, which would be answered by Itachi's Susanoo, which would completely negate Kakuzu's chance of winning this match. A close up combat with a Sharingan user is never a good idea. If Kakuzu isn't taken out via Genjutsu or through a sneak attack in the close combat part of the match, he'd end up pulling out the masks, which would probably push Itachi to use the Susanoo, which he would use to take out Kakuzu. Other than that, Itachi could always simply use the Amaterasu, which Kakuzu has no counter for whatsoever.