That is significant because Klopp's style of football is extremely taxing, but it becomes particularly important now they are contenders in the two biggest competitions going into the second half of the season.
And in qualifying for the last 16, Van Dijk feels his side showed their quality in the home matches and feels they could have scored more against the side now second in Serie A.
Liverpool met Italian opposition last season at the semi-final stage in this competition beating Roma 5-2 at Anfield and 7-6 on aggregate. "We created two good ones but didn't have the luck we needed to put them in the back of the net".
"And, yes, that save was just incredible, but if we don't defend the whole pitch like we defended, Ali can not make 20 saves like the last one".
But what I do know is that they will give it a really good go and, with the squad that Klopp has built, they are well equipped this time to build on the position they have put themselves in.
Financially, the club is in great shape too. The intensity we played with was hard to play against.More news: US Must Not Interfere in French Politics
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"We could have scored more, but the last chance Sadio Mane had made no difference in the standings".
Mohamed Salah's duel with Napoli center-back Kalidou Koulibaly was tipped to be one of the most interesting match-ups of the night and the battle stayed true to its billing as the pair faced off several times during the match.
The ball was cleared, then following a flag for offside during the next passage of play, Virgil Van Dijk made a beeline for the floored shot-stopper, and passionately shook him in a moment of fiery affection, much to the delight of the fans. He is the sort of manager who sees his squad as people, not just players, and it is paying off.
Assailed by doubters who claimed he has lost his love of the game, Mohamed Salah produced the ideal response as he fired Liverpool into the last 16 with a virtuoso strike that recalled the best days of his debut campaign.
Instead, they managed the occasion.
Liverpool have lost one of the last 23 European games at Anfield and are unbeaten in the last 18 at home, winning 13 and drawing five since losing 3-0 to Real Madrid in October 2014.
Their success so far is down to the whole team, not just any one department. "I am really proud of what the boys did". While the highly rated Senegal worldwide tried to contain the sixth best player in the world, it was one of their meetings on the left side of Napoli's defence that birthed the decisive goal.
This season Napoli have drawn both Champions League games away from home, playing out a goalless draw in Belgrade and drawing 2-2 in Paris.
A week after lambasting Burnley for their physical approach during Liverpool's 3-1 win at Turf Moor, Jurgen Klopp can not now argue that Van Dijk's tackle was clean and fair if he wants to be seen as being consistent on his view of challenges during a game. "I heard it after the game so I was a bit disappointed about that".