France international Anthony Martial broke the deadlock in the first half from the penalty spot after Nathaniel Clyne brought down the United striker.
Liverpool had more energy and pace but still not great performance from them
However, Philippe Coutinho levelled the last-16 tie on the night with a brilliant finish that the Liverpool midfielder lifted over David De Gea.
Klopp’s side edged a stop closer to the Europa League final thanks to their 3-1 aggregate win against the 20-time English champions after a 2-0 win at Anfield last week.
However, former United captain Keane rubbished the suggestion that the current Liverpool crop have the hallmarks of a potentially great Reds side.
“This still isn’t a great Liverpool team,” Keane told ITV Sport.
“The qualify from both sides was poor. Liverpool had more energy and pace but still not great performance from them. But over the two legs, they still could have scored eight or nine goals.”
Liverpool are in eighth place in the Premier League table and seven points behind fourth-placed Manchester City in the race to secure a spot in next season’s Champions League.
The Merseyside outfit are in action against Southampton on Sunday afternoon.
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