Another victory will clinch the series for the tourists who will seek to start the game the way they finished the first Test.
The Lions trailed 12-3 at the interval last Saturday but won the second half 19-5 to turn the game around.
Warren Gatland liked the way his side grew in strength and it is reflected in the changes made by the head coach. Daly, who has played little Test rugby at outside centre, makes way for Harris who was not involved in the first Test.
Conor Murray, a second-half substitute on Saturday, replaces Ali Price as the starting scrum-half, with the Scotland man dropping to the bench. It’s tough luck on Price who did little wrong against the Springboks and seemed to grow as the game went on.
Rory Sutherland also finds himself on the bench, replaced at loosehead by Mako Vunipola who added solidity to the scrum when he replaced the Scot in the second half of the first Test.
And there was one more blow for Scottish Lions, with Hamish Watson dropping out of the matchday 23 altogether, Gatland opting instead for Wales No 8 Taulupe Faletau as back-row replacement cover.
The good news is that Stuart Hogg and Duhan van der Merwe retain their places at full-back and left-wing respectively and they are joined in the back division by Harris whose late development as an international player now looks complete.
The Cumbrian Scot was 27 when Townsend gave him his first Scotland start and will be 30 on the occasion of his Lions Test debut. If his international career has been something of a slow burn, his performances in this year’s Six Nations marked him out as one of the best defensive centres in the northern hemisphere.
“I’ve got a lot to thank Gregor for for giving me that first opportunity back in 2017,” Harris said. “It was a bit of a slowish start, I didn’t pick up too many caps in my first year but he still gave me opportunities. I’m obviously grateful that he did, it’s worked out pretty well for me.”
Townsend’s role as the Lions attack guru and the involvement of another Scotland coach, Steve Tandy, as defence expert, means there are strong Scottish voices in the selection meetings but Harris believes his form speaks for itself.
“I’m not in that selection room. I’d like to think my playing did the talking,” he added. “Obviously Gregor and Steve both know me better than the other coaches do, so maybe it has helped my chances. But I’d like to think it’s me as a player that’s shown Gats and the other coaches that I deserve the opportunity.
“I am over the moon. I was a bit taken aback when my name was read out by Warren.
“I didn’t really have any inkling. Obviously when a team wins you think they will go with a similar sort of team but maybe a couple of changes. We had training in the day and it was hard to tell what the team would potentially be. It was a surprise, a nice surprise, and I am really delighted.”
Harris said he would embrace the challenge and did not feel awed by the prospect of joining a winning team with so much on the line.
“Pressure is a privilege isn’t it? It is an opportunity for me to go out there and really show what I am about and contribute my game to the team and hope we can come away with another win.
“I welcome the physical side of the game, the way that South Africa want to play suits me as well. It’s an opportunity for me to really show what I'm about and get stuck in.”
Harris said Daly had been gracious in accepting his demotion to the bench.
“I was sitting next to him when the team was announced and he was the first to congratulate me,” explained the Scotland centre. “It was a similar thing for me last week when the team was named. I wasn’t named in the squad at all and I felt really deflated but it is part of professional sport and this environment. Some of the boys are going to miss out and it is all about how you are going to react to it.
“I congratulated Elliot last week and he congratulated me this week. That is just the way it is. It is how you react and have to go out and try as hard as you can.
“If you react the other way, you become a bit bitter and you switch off and it doesn’t look good on you and you are not testing the team that is going to go out there and play against South Africa.”
Finn Russell is back training with the squad after recovering from an Achilles tear and although he has not been selected for the second Test, Harris is hoping his Scotland midfield partner gets the nod for the third match against the Springboks on Saturday week.
“It would be brilliant for Finn,” said Harris. “He’s back training and looking very sharp. I’m not picking the team but it would be great for him to be involved.”