The experienced Irish back row man gets his latest chance to impress at the Absa Stadium and try to follow in the footsteps of his elder brother Paul in making a Lions Test side in South Africa.
Paul was the tight head prop in the three tests in 1997 when the Lions won the series 2-1. His eldest brother, Richard, also toured with the Lions in New Zealand in 1993.
But if he is to make the team for the vital first Test against the Springboks he knows he needs to come to terms with the subtle changes in the laws, and interpretation of them, at the breakdown.
The Lions turned over 14 balls in their opening game against the Royal XV and exceeded that number in their two point win over the Free State Cheetahs last weekend. Wallace played at No 8 in the opening game, but will be back in his specialist position of openside flanker tonight.
"There is a big onus on me, but also on every other player on the pitch. There are only so many rucks you can be involved in, so it is something for the whole team to concentrate on," said Wallace.
"Everyone has the ability to steal the ball or slow it down for the opposition. The fact you can now get in there and stay there means it doesn't really matter what jersey number you are wearing
"It certainly is a lot more difficult area than it was since they made the law change. In some ways it is a good ruling because the exponents who can get in there, can fight for the ball and stay on their feet get the chance to try to rob some ball.
"Before, it could be an easy out for the referee to shout 'it's a ruck, hands away'. Now the onus is on the opposition to actually get rid of the player.
"If he is on his feet, then he is legal. It makes things a bit harder and is quite a mind shift in terms of how you approach the game and get numbers there."
But the one factor the Lions haven't been able to control so far on tour has been the new interpretation of the referees. England's Wayne Barnes flummoxed many with his rulings in Bloemfontein last weekend and those of Jonathan Kaplan tonight will be critical to the Lions' chances.
"You have to ride the referees and see what you can get away with. You have to react on the pitch," said Wallace.
"It is not just about numbers at the breakdown, but about quality and what you do when you are there. If you get it right you shouldn't need more than two or three players."