Liverpool also registered their fifth clean sheet in six home league matches, with Alexander-Arnold impressing as he continued his rotation at right-back with Joe Gomez.
"He was really good, it one of his best performances over 90 minutes in defending. What he can do offensively everybody knows," Klopp is quoted by Sky Sports News as saying.
"When he started he was a proper winger and sometimes a defender, and now he is a proper defender and sometimes a winger and that makes much more sense for this position."
Alexander-Arnold has made 21 appearances for Liverpool's senior team since making his debut last season.