Bangladesh bowled out for 233 to lose by 149 runs
Mahmudullah makes excellent 111 off as many balls to defy South Africa
South Africa post imposing 382-5 after late flurry
De Kock hits sublime 174 off 140 balls - highest score in tournament
Klaasen smacks 90 off 49, Markram adds 60 off 69 & Miller cracks 34* off 15
Proteas move up to second in the table, Tigers now bottom
Time for us to leave it there for today.
You can scroll back through this page for the thoughts of both captains and some of the best moments.
We'll be back at 09:15 BST on Wednesday for Australia against the Netherlands.
See you then.
South Africa captain Aiden Markram: "It was another good day. Tough to grind it out at the end, but we thought sticking to what we believe in would take 10 wickets. Sometimes you can rush it. But all in all a great day."
On whether South Africa have an issue with death bowling: "Not neccesarily. Sometimes we found ourselves in two minds, whether to go to death bowling or not. They guys have worked quite hard on their death bowling, had some great plans and it is a case of going out there and hoping they execute them.
"Mahmudullah played fantastically well. You are never practicising in a match but we thought we would switch to death bowling with him, but if it goes wrong the ball tends to disappear."
On South Africa's batting: "What Quinton did was superb and then Klaasen smashes it like we know he can. The top six/seven are different in their approach but it gels quite nicely. We will keep striving to put in big performances each game."
On whether South Africa prefer batting first over chasing: "Not neccesarily. We had a chat and the majority preferred chasing. It is just the way things have come. The more you win batting first the more you believe you are that team but I don't think that is the case with us. Once we get one chase under our belts the belief will come back and we can be a good team that chases as well."
On Temba Bavuma's fitness: "He has improved quite a lot but wasn't quite ready for today. Hopefully he can keep improving and be ready for Pakistan."
Bangladesh captain Shakib Al Hasan: "Yes, I thought we bowled well for the first 25 overs, got three wickets and they were going at five-an-over.
"Then they kicked on, I thought Quinton de Kock batted really well and the way Heinrich Klaasen finished it off, we didn't have any answers to it.
"We conceded 144 from last 10 overs, which is probably the most expensive 10 overs we've bowled in the last 10-15 years. But on a ground like this, it can happen like that.
"We should have bowled better but we lost our plans in the last 10 overs. That's where we lost the game.
"There has been a lot of talk about whether Mushfiqur and Mahmudullah should bat up the order. They're doing their roles well but our top four or five are not scoring runs, need to score more runs so we can get more out of them.
"South Africa, India and New Zealand are the three teams that look like they can win the title. But anything can happen, someone can pick up halfway through and go all the way. There's still a long way to go.
"There is a lot to learn and a lot to play for. For the Champions Trophy, we have to be in the top eight and that's important.
"We'd still like to finish up the table, if not semi-finalists then fifth or sixth. We're not playing like a team that can do it but I'm still hopeful we can come back strong to finish the tournament."
South Africa are now well-placed to reach the semi-finals.
They next play on Friday, 27 October against Pakistan, before games against New Zealand (1 Nov), India (5 Nov) and Afghanistan (10 Nov). You would expect two more wins would definitely see them through. One may even do it.
Bangladesh now face a tough challenge to reach the final four but aren't mathematically out of it yet. They face the Netherlands on Saturday (28 Oct) and then Pakistan (31 Oct), Sri Lanka (6 Nov) and Australia (11 Nov)
South Africa's power at the end of their batting innings was undoubtedly the difference again.
They added 144 in the last 10 overs with Heinrich Klaasen smashing 90.
South Africa have now posted the three highest scores in the tournament.
A special mention for Mahmudullah too, who made a very good century in defeat.
Here's the winning moment.
It was a pretty sedate celebration from South Africa, who will probably feel like they should have wrapped this game up a lot earlier than they did.
Player of the match Quinton de Kock: "To be honest I am a bit more tired than satisfied. It was a great day out for the guys. Everyone did their part and it is nice to get another two points on the board.
"I was little bit nervous this morning, but it was great day. I had a bit of fun and it is great to get another two points."
On Heinrich Klaasen: "He has been amazing, I need some of the juice he is having! He has been really special this year and long may it carry on. He is taking it by storm and I am really happy for him."
This is how the table looks after that result.
Today was only match 23 of 45 in the group stage, but we are already seeing three teams - India, South Africa and New Zealand - pulling clear at the top. They look likely to reach the semi-finals.
But who will join them?
Image source, BBC Sport
Jonathan Agnew
BBC cricket correspondent on Test Match Special
South Africa are are not walking off with the big high fives they might have done if they won an hour ago. They have been given something to think about.
I can confirm that England are no longer bottom of the table.
Bangladesh now are.
I'll bring you the full table shortly.
The Proteas pick up their fourth win, and in comfortable style.
Lizaad Williams wraps up the innings as Mistafizur sends one up in the air and David Miller settles under it to take the catch.
It sees South Africa climb above New Zealand, into second behind India.
Text 81111 (UK only - standard message rates apply)
Cricket needs to choose between 50 and 20 overs, it cannot sustain both. I loathe 20/20 but obviously it would be 50 over cricket that needs to go. Test cricket is sacred.
George, London
Here's how Mahmudullah brought up his century. It clearly meant a lot to him.
Mahmudullah c Jansen b Coetzee 111 (Ban 227-9)
South Africa have finally found a wicket.
It is full from Gerald Coetzee and Mahmudullah tries to drill it over the covers but can only pick out Marco Jansen.
Coetzee gives Mahmudullah a little clap and a few others give him a fist bump on the way off too.
It has been a very good innings and saved Bangladesh from a record defeat.
Steven Finn
Former England bowler on BBC Test Match Special
I think South Africa have missed Anrich Nortje in this situation, like they did against England the other day.
When I played in successful teams we knew we had to send a message and kill the tail.
This is expending both physical and mental energy for South Africa.
South Africa have got sloppy.
Kagiso Rabada oversteps but again Mustafizur Rahman is unable to take advantage of the free hit.
The Proteas have to be concerned about the second half of this innings, surely.
Steven Finn
Former England bowler on BBC Test Match Special
This is an excellent innings from Mahmudullah. He has played some lovely shots and you can see what it means to him and his team-mates.
Six more.
A knee-high full toss from Kagiso Rabada and Mahmudullah dispatches it over mid-wicket.
Well played, Mahmudullah.
He reaches a brilliant World Cup century off 104 balls with 10 fours and three sixes.
It will be in a losing cause but fair play to him. He jumps in celebration and thumps the badge on his shirt.