Master Hand was just playing around there. He probably was underestimating Tabuu's power, and as a result, didn't go full power himself.
Think about it like this: The Smashers beat Tabuu, but it's already been established that the Smashers are nothing in comparison to Master Hand, and he's simply playing around with them, like a father would his son, and from that, we can assume that a full power Master Hand could beat a full power Tabuu.
The only reason that Master Hand didn't win that battle was probably because Master Hand got caught off guard, thus, in that brief period of time, getting "imprisoned" by Tabuu, and after being stuck like that for months, being unable to break free, as you don't even know what's keeping you stuck there in the first place, you start to get drained, and desperate, thus, causing Master Hand to eventually mindlessly charge at Tabuu, not letting his better judgement stop him, which eventually led to his temporary defeat (but unlike Tabuu, Master Hand is an immortal being that cannot be killed)
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Edit: I forgot to hit the post reply button, so, as a result, U-throw beat me to the chase, but, we have different explanations, so I'll keep this post here