<p>No version of Gaara can defeat Itachi.
</p><p>His sand shield is completely irrelevant because totsuka blade is basically a ghost sword. It's going through his shield, and when it does Gaara won't see it coming because Itachi is faster and smarter than he is being given credit for.
</p><p>Itachi still has an incredible actions per second magnitude . In the time it took for him to sheath shurikens, he already weaved the signs for three separate techniques: a water technique, a shadow clone technique, and a substitution technique. Itachi's technique speed is still something that keeps him in the game against many top tier shinobi, so factor in yata and totsuka hax and there is nothing gaara can do.
</p><p>This fight ends before it begins. The totsuka blade was so fast that orochimaru nor nagato could mentally process it. Think about that. The optic nerves in their eyes didn't have enough time to communicate to their brains that there was a giant blade speeding toward them. Nagato couldn't take any mental or physical action to block/evade the blade despite having a wide arsenal of techniques at his behest that could have potentially done it.
</p><p>So, even in the desert, Itachi can simply genjutsu the eye as people have already stated. alternatively, all he has to do is wait until gaara forms his sand shell. when Gaara sends a tsunami of sand at him, Gaara will still be blinded by his own sand, third eye or not. Gaara is still kind of a stationary fighter... so itachi just has to mark his position with the sharingan then launch the blade through all the sand, and Gaara is one shotted.
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Itachi also has high mobility and isn't just gonna stand there wasting his chakra. Yata mirror stops any of the sand attacks anyway lol.
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