The Senegal international had been out of action for a month after suffering a hamstring injury while on international duty in October. Klopp suggested on Friday (3 November) that the winger was only ready to play as a substitute at West Ham after having only returned to full training on Thursday.
But the Liverpool boss surprisingly handed him a starting role in a new 4-4-2 formation with Mohamed Salah and Roberto Firmino leading the attack.
"Sadio is a naturally fit player, he is a little machine," Klopp said in the press conference following the 4-1 victory at West Ham.
"When we trained after the Maribor game on Thursday, [he] was a little bit stiff in the beginning but then you can see he starts enjoying the intensity. That's why we decided we should try it. I asked him because I could not see how he felt after that session. I said in the press conference yesterday he is ready for 25 minutes, but obviously he was ready for 25 minutes plus. That's good for us."
"We had a few very difficult things to decide since yesterday. Bringing Sadio Mane in from the beginning after his injury, after one session and then yesterday the second session with the team, I never did it before, to be honest. Obviously it was not the worst idea I've ever had! We changed the system and yesterday was the first time we did it, 4-4-2, which looked maybe from the beginning like a very offensive line-up, we had a different idea - we wanted to defend deeper, more compact and using the space which we had for the counter-attacks,
"We will never know how it would have been if we don't score the first one, I think it was kind of an open game up until then. We had to get used to it a little bit, it was difficult for the boys to wait a little bit more for the challenge than jump always."
Mane looked fully fit as he assisted Salah for Liverpool's first and fourth goal, before being replaced by James Milner in the 77th minute of the game.
However, Klopp admitted his worries ahead of the coming internationals with the Liverpool star being now set to join up with Senegal for two crucial World Cup qualifiers with South Africa.
"I am always worried, to be honest. It is the most difficult time for me. [Injuries] can happen every day; it can happen in our training, in their training, it can happen in a game, but that's how it is. I have no problems with international games, I'm really happy for Senegal that they could go to the World Cup and they need Sadio Mane for this, I understand, he is fit to play," Klopp admitted.
"The only thing I would ask is if they can make it in the first game then it would be cool if he could come back and could make the preparations for our game against Southampton. I cannot decide things like this, I don't even try, but we are in contact. First, he goes there and he recovers and has a long flight, then he will play the game, good news for Senegal. He needs real recovery - if you know the coach of Senegal, tell him - after this game today and then he will be ready for South Africa."
Meanwhile, the Liverpool boss revealed that he was also force to change his original plans in the midfield due to the injury of Jordan Henderson and the unexpected recovery of Georginio Wijnaldum.
The captain couldn't even make the squad after suffering a thigh injury on Friday, while the Dutchman started and played the full 90 minutes, despite being originally ruled out.
"The day didn't start well. We did all the tactical things yesterday with the new system and with Jordan on the No.6. He told me he could play, but unfortunately the medical department thought a little bit different. After a week like this, it is normal the players feel a little bit with their muscles. I had to make this decision and he was not in the squad. If he cannot start then you cannot bring him in and then after 10 minutes we have to make another change. Maybe he could have [played], I am not sure," the Liverpool boss revealed.
"It was not the best news I got today, but it was even more funny because Gini Wijnaldum tried yesterday and after training we said no chance. Then overnight he improved. We took him with us, but only to be closer to the doctor. He had no boots. This morning he had improved a lot so we could try, we only had to organise boots. I'm not sure where we got them from!"