England's hopes of keeping the three-match series alive were ended as they slipped to a battling 36-27 defeat in the second Test in Johannesburg.
The Springboks now have an unassailable 2-0 lead heading to Port Elizabeth for the next encounter but Lancaster feels his side will soon pick themselves up.
He said: "Our boys have had an 11-month season now - it was probably this time last year the World Cup camp started.
"We went through that, the World Cup, the Six Nations - it has been a long slog - but I guarantee there is one more game left in them.
"The good thing is the overriding feeling in the dressing room was frustration.
"I would be disappointed if the players came in and said, 'We did a good job and almost won'.
"Great sides want to win all the time and these players are hungry.
"We'll bottle the frustration, drive it through training this week and then have a crack at it in Port Elizabeth. That is the great part of this three-game series."
England proved their defensive resilience in the narrow 22-17 first Test loss in Durban but they were lacking in that area as the Springboks raced ahead in the capital.
Backed by an intimidating crowd at the spiritual home of South African rugby - the ground formerly known as Ellis Park, now Coca-Cola Park - the hosts powered forward to take a 22-3 lead inside 19 minutes.
With the Springboks winning the forwards battle emphatically, the tourists faced a possible landslide defeat but a breakaway Toby Flood try stemmed the tide.
Two opportunistic touchdowns from scrum-half Ben Youngs remarkably - given South Africa's earlier superiority - saw England get back within four points but JP Pietersen ended the fightback.
Lancaster said: "I thought our scrum began to take control and gain the ascendancy in the second half.
"When we had the ball and we moved the ball we definitely caused them problems defensively.
"But when the Springboks have the ball they run hard at you and it is hard to stop. They move the ball well.
"I thought in some areas we were better and others we weren't, but that is part of coaching and rugby at this level.
"We will definitely take the positives but the areas we need to develop we will have a good look at.
"It would help if we didn't give them a start but we can win in Port Elizabeth.
"As soon as your belief goes it is going to be a difficult mountain to climb."
The defensive issues will be one of the main areas of concern but Lancaster will revisit the issue of bringing in a specialist coach in that area after the tour.
Andy Farrell earned widespread praise for his role while on secondment to England from Saracens during the RBS 6 Nations but turned down the offer of a full-time role.
The former rugby league star's recent resignation from Saracens has sparked speculation he may yet link up with England after all but that remains to be seen.
Lancaster said: "I got the job about six weeks ago.
"We have come a long way since the start of the Six Nations, when I was on an interim job.
"I said before we came on tour I would look at the coaching situation after the tour and that remains the situation.
"We are working our socks off. We have a game on Tuesday night and that is the next thing on our minds, and getting this team picked up and ready to go again on Saturday."
Lancaster's selection for Port Elizabeth could yet be influenced by Tuesday's run-out for the second string against the Northern Barbarians in Potchefstroom.
He said: "It is too early to say. I have had some quick thoughts but the first thoughts are getting from the problem to the solution.
"We wanted to come on this tour and give the players some experience and also learn about players."
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