Reds skipper Gary Neville says Liverpool's comprehensive defeat to Everton on Saturday inspired United to battle to victory against Tottenham later that day.
The Reds earned a narrow victory over Spurs with a goal from the in-form Ryan Giggs. But the United squad had earlier watched Liverpool lose 3-0 in the Merseyside Derby, a result Neville and his team-mates believed was influenced by the tiring recent international break.
"We watched the Merseyside derby and it made us realise just how difficult it is for the top teams immediately after an international matches," he said.
"You tend to get back home at 5 or 6am on the Thursday morning but your legs don't seem to come back with you.
"Some of the lads had not even trained. It's always a difficult situation and you have to just dig in and get the win."
It was at this point last season that United drew with Manchester City on the back of an international break. But, having made it four wins out of four - the Reds' best ever start to a Premiership campaign - confidence is growing within the squad. But Neville says greater challenges lie ahead.
"We've won all of our games," he said. "So, at this stage, we couldn't have done any more. But we're aware it is still early days and there are tougher tests still to come."
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