Bayer Leverkusen coach Xabi Alonso hailed Liverpool's quality after the German champions were blown away in the second half of a 4-0 loss at Anfield in the Champions League on Tuesday.

Alonso had been one of the leading candidates to return to his old club when Jurgen Klopp stepped down as manager at the end of last season.

The Spaniard's decision to remain in Germany opened the door for Arne Slot to take charge and the Dutchman is off to a flying start with 14 wins and one draw in his first 16 matches in charge in all competitions.

Liverpool are sitting pretty at the top of both the Premier League and Champions League and have advanced to the quarterfinals of the League Cup.

Leverkusen matched the Reds for the opening hour but collapsed after Luis Diaz latched onto Curtis Jones' through ball to open the scoring.

Cody Gakpo quickly headed in a second before Diaz struck twice more in the final 10 minutes for his first Liverpool hat-trick.

"They are a complete team," said Alonso, whose name was chanted by the home fans in the closing stages.

"They are able to defend, to score, to have power in the boxes, keep clean sheets, with not many chances to score goals - that is a great strength in the Champions League.

"They are in a good moment, everything has good balance, the coach is doing great work, so it looks like a great season but we are still in November."

Liverpool were inspired by the atmosphere to come from behind to beat Brighton to go top of the Premier League on Saturday and relied upon a similar boost from the crowd after a flat first half.

Alonso won the Champions League during his five years as a Liverpool player between 2004 and 2009 and said he was powerless to stop that momentum despite his personal experience of the Anfield crowd.

"I know the feeling that the Liverpool players they feel. It is an extra boost, 'now is the moment, now we go'," he added.

"To defend in those moments is not easy. Like what happened to Brighton on Saturday. To put it in words is easy, it's much more difficult on the pitch."

Slot's midas touch saw his decision to start Diaz in an unfamiliar central role up front rewarded as the Colombian scored the first hat-trick of his career.

Diaz has had to battle with Gakpo for a regular starting role this season but is already up to nine goals for the campaign.

"It's a very special moment that I'll remember my whole life," said Diaz.

"They are a very tough opponent. It was about trying to turn the game in any way possible.

"The first goal then opened the game a bit and we were then able to play our game. We had a super second half." (AFP)