Steward at full-back for England, Marler and Martin start against Springboks
Ellis Genge and Ollie Chessum move to the bench but there is no place in the squad for Marcus Smith, who was ruled out after failing a Head Injury Assessment earlier in the week following the head collision he suffered early in the Fiji quarter-final.
Steward, England's back-to-back player of the year, is one of the best under the high ball in the game and a sturdy defender. France struggled to deal with South Africa's aerial bombardment in their quarter-final but Steward will back his abilities and would have likely started even if Smith was fit.
He had played 28 consecutive matches before being rested for the Chile game. He returned for the final pool match against Samoa before missing out versus Fiji.
Borthwick saw something in Steward's face when he did not pick him for his first game in charge of Leicester early in 2020.
"I realised that he wants it and he's ready no matter how old he is," he said. "I put him in the next week and he's been brilliant ever since."
Loosehead prop Marler and lock Martin, making his second start of the tournament, have been brought in to help beef up England's scrum against a South Africa pack who were impressively strong against France.
Martin, a surprise teenage call-up under Eddie Jones in 2021, is another who Borthwick has mentored since his academy days at Leicester.
"I've known him from being a very young man to someone who looks very much at home on the international stage," he said.
"He's come (into the team) in two positions (flanker and lock) during this tournament and performed in some key moments.
"Every challenge I've put in front of him he's embraced it and ripped right into it. The front row boys are pretty positive about how much weight George gives them in the scrum."
SEEKING REVENGE
England go into the game seeking revenge for the 2019 final defeat by the Springboks and hoping to earn a showdown against New Zealand or Argentina, who meet in the other semi on Friday.
But while 13 of Saturday's England squad played in that 32-12 final loss, everyone in the camp is playing down the significance of what happened four years ago and stressing the challenge of the current threat the world champions bring.
"They have their traditional power of set piece, their contestable kicking game is another great strength and they’ve layered on ball movement and speed on the edges," Borthwick said.
"We know the intensity of the match will be incredible but we are focusing on ourselves. We have been building our team towards this."
Captain Owen Farrell said that despite external criticism of some of England's performances in their five wins in France and the undoubted quality of their next opposition, there has been nothing radical in their preparation.
"We've just talked about embracing it, getting he best out our ourselves," he said.
"There's not necessarily anything new or out of the ordinary - we have a lot of players in this team who know how to win big games."
Saturday will be the teams' sixth meeting in World Cups, with South Africa winning the previous four knockout games, including two finals. England's sole success came in a 2003 pool match - the only time they managed a try in the five clashes.
England: 15-Freddie Steward, 14-Jonny May, 13-Joe Marchant, 12-Manu Tuilagi, 11-Elliot Daly, 10-Owen Farrell (captain), 9-Alex Mitchell, 8-Ben Earl, 7-Tom Curry, 6-Courtney Lawes, 5-George Martin, 4-Maro Itoje, 3-Dan Cole, 2-Jamie George, 1-Joe Marler.
Replacements: 16-Theo Dan, 17-Ellis Genge, 18-Kyle Sinckler, 19-Ollie Chessum, 20-Billy Vunipola, 21-Danny Care, 22-George Ford, 23-Ollie Lawrence