Victory for the world champions at a stadium where they have won 71 per cent of their games would secure Test series glory with one match still remaining.
The Lions, in contrast, are fighting to stay alive following a 26-21 defeat in Durban last Saturday.
But forwards coach Gatland saw enough in the Lions' second-half performance - they fought back from 26-7 adrift - to confirm his belief the series is far from over.
And the Wales boss was not afraid to criticise South Africa's style of rugby as the Lions left their Cape Town base for a return to the Highveld.
"The South Africans have very much a bully mentality, to come in and try to dominate, pushing players off the ball," he said.
"You saw (Bryan) Habana getting into a player's face, and you saw (Bismarck) du Plessis.
"I would be very surprised if any of the Lions players take a backward step to any physical threat imposed by the South Africans.
"One of the things that surprised me about South Africa was how little rugby they played.
"They went to fourth phase once in the game, and I think the centres got one pass.
"There has always been a lot of criticism about northern hemisphere rugby, about us being quite boring and playing 10-man rugby.
"You wouldn't often give that criticism to teams like South Africa, but they didn't play any rugby at all."
South Africa, with their pack in dominant mode, powered to an unassailable lead, capitalising on the destructive scrummaging power of Tendai "The Beast" Mtawarira and another immaculate display by revered lineout forwards Bakkies Botha and Victor Matfield.
Head coach Ian McGeechan has responded to particular problems in the scrum and coping with South Africa's driving maul by changing 60% of the front-five.
Gethin Jenkins, Matthew Rees and Adam Jones forge the Lions' first all-Welsh Test front-row since 1955, while 19 stone lock Simon Shaw's long wait for a Test place has ended just two months before his 36th birthday.
Ireland Grand Slam backs Rob Kearney and Luke Fitzgerald also enter the equation this weekend, but whether it is enough to prevent a record seventh successive Test loss on tour remains unlikely.
The Lions, though, will not throw in the towel wondering what might have been.
If they can secure enough possession, the emphasis will again be on all-out attack based around their world-class centre combination of Brian O'Driscoll and Jamie Roberts.
And the Lions will also hope for what Gatland described as "a fair crack" from the match officials, who are this week led by French referee Christophe Berdos.
"You get a touch judge's decision on Matthew Rees for throwing a punch," Gatland added.
"We've had a look at it, he's swung with the arm but no contact has been made, so you just want a break and to get some 50-50 calls.
"We are not asking for any favouritism, just giving us an opportunity to play.
"South Africa didn't have to play a lot of rugby. We gifted them a number of points and we missed three or four real scoring opportunities ourselves.
"They played winning Test match rugby, but they didn't play any rugby.
"There is a possibility that they may go out and throw a bit more ball around, but we didn't put them under enough pressure for them to have to do that last weekend.
"We've got to be in the game in that first 20 or 30 minutes. We just can't afford to go behind by 10 points or more against South Africa.
"We were very pleased with the way we finished the game. We dominated in the last 20 minutes, but it is really important we start well and negate their physical threat against us.
"We have to make sure our discipline is good and we don't give away any stupid penalties. We have got to scrummage well, our lineout has got to be accurate and we've got to be smart in the way we play.
"But we are not talking about sitting back. There is definitely no threat of us sitting back and playing negatively - we've got to go out and get stuck in as well."
If the Lions could deliver a series-levelling result, it would rank among the finest in their 118-year history.
But a Springboks team likely to be better than last week, plus a first game at altitude for the Lions in three weeks, means the odds are stacked against them.
Gatland insisted: "We think physically we are in great shape.
"We take a lot of heart out of the last 20 minutes (in Durban) when we had 80% of territory and possession and scored 14 points.
"We felt the South Africans were the team out on their feet, they were the guys with their hands on their knees and struggling with the game."
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