United dominated the first half but rarely threatened Karius' goal and the German kept a clean sheet for the first time since replacing Simon Mignolet in goal.
David De Gea made two incredible saves but United defended well and didn't allow Liverpool many chances.
"They know we're a really strong team, so that's a compliment for us," Karius said.
"United maybe waited for the one chance to get a goal, as obviously their priority was to stop our play, our attacks.
"We knew we had to be patient because it was going to be tough.
"Second half we managed better to get through but United defended well with De Gea making top saves."
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