Stewart hails Collingwood spirit
Paul Collingwood and Jonathan Trott shared a partnership of 162 as England won by seven wickets at Centurion.
Stewart told BBC London 94.9: "They're consistently inconsistent and they've got to shed that.
"But what impressed me, Collingwood and Trott played cricket shots, and they played as proper batsmen."
He added: "They hit strong cricket shots down the ground and then if it was short they hit it square of the wicket.
"They didn't start reverse sweeping and doing all these things unless it was necessary, a lot of the time people get to 15 and 20 and suddenly they reverse sweep, top edge and get caught.
"Why don't you just hit the gaps into extra-cover, until you've built momentum and are constructing an innings?
"The two of them both set their sights on scoring a hundred and being there at the end, Collingwood achieved it and Trott nearly achieved that.
"That's been the biggest thing, if you look around the world at the successful sides, you have batsman who put their hands up and say: 'I will score a hundred, and I will do that through good, solid batting.'
"England haven't scored enough hundreds ever in one-day cricket, certainly not in recent times, and hopefully the rest of the team, and the players that will come into the side in the future, will have looked at the Collingwood and Trott partnership and said 'that's how we've got to play.'
"That's why England's one-day form is so frustrating, because when they play like that, as they did on Sunday, they will beat anyone.
"Collingwood led the way, ably supported by Trott. In the field, just forget the captain spilling a few chances, but I thought they were good and the bowing was efficient. They destroyed South Africa, yet we may see a different England in the next two one-day games coming up on Friday and Sunday.
"You just don't know what England side is going to turn up and that's why they're so frustrating, but also when they get it right, whether it's in a series against South Africa or whether it's a world tournament, you can never write them off but you can never also put them as favourites."
Collingwood, who scored an unbeaten 105, also broke Stewart's one-day appearance record for England by winning his 171st cap and Stewart, now on the coaching staff at Surrey, says he could not think of a better person to have passed the milestone than the 33-year-old Durham batsman.
"It's amazing really, when he made his debut I was captain," said Stewart. "He's a cricketer, who probably isn't appreciated as much as I think he should be. Without appearing rude, he's probably not the most flamboyant cricketer, but he's exceptionally effective.
"I'm very pleased that it was him that broke the record and he will go on to get many, many more caps.
"As a fielder, in my opinion, he's certainly in the top three fielders in world cricket today. As a batsman, when your backs are against the wall, you want him out there, and I've always called him a Steve Waugh type of cricketer.
"Mark Waugh was, let's say, the better looking, prettier cricketer, but Steve was the more effective and I put Paul Collingwood in that bracket, which I hope he takes as a huge compliment.
"As a bowler in one-day cricket, he's very, very handy. He's someone who has learnt over the years to mix up his style of bowling and the experience he brings to the team makes him a vital component."
England lead South Africa 1-0 in the five-match series going into Friday's third match in Cape Town, but Stewart says England must beware a back-lash from the hosts, led by their captain Graeme Smith.
"I'm going back to 2003, Graeme Smith was the most impressive young captain that I've ever come across, whether it's past or present," said Stewart.
"He really has impressed me, he's led from the front and he knows exactly what he wants. He's now a more mature captain, he understands international cricket much better, so now he'll be making sure that his team are fired up, that they perform, that he performs and that they put England under pressure from ball one."