And forwards coach Gatland has been impressed with the way training has progressed following a stunning end to the first Test defeat in Durban.
"We've trained well this week and the players are looking sharp," said Gatland, who saw the Lions fight back from a 26-7 deficit only to lose 26-21 to the Springboks first time around.
"Physically we are in good shape and we aren't concerned about playing at altitude. We had 80% territory and scored 14 points in the last 20 minutes in Durban when they were out on their knees. That's why they've got a 5-2 split between forwards and backs on their bench.
"Test match rugby is about taking chances and we didn't do that last week. We have to this time."
Gatland, who played against the Lions for his native Waikato in 1993, has made it clear to his players that a good start is vital if the Lions wish to come away with a win this afternoon.
The Wales head coach knows the Lions cannot afford to give the Springboks the 13-point head start they gifted them eight days ago - not if the tourists want to avoid the same outcome for a second week running.
"The key to the game is being in it for the first 20 or 30 minutes," added Gatland.
"We simply can't afford to go behind like we did last weekend. I was happy with the way we dominated the last 30 minutes, but our discipline and accuracy have to be good this week.
"We have got to be smart in the way we play in the first 30 minutes. The players we have brought in are very much aware of the need for a good start - we won't be sitting back.
"We have to go out there and get stuck in. Our scrum has got to be solid and we need good line-out ball. We conceded two scrum penalties on our own put-in last week, which cost us six points, and we lost three line-outs. We mustn't give away any daft penalties this week.
"South African teams have a bullying mentality and they like to come in a push you around and off the ball. But I would be very surprised if any of the Lions took a backward step."