Dernbach claimed three big wickets in an under-par South African batting performance that saw the tourists bowled out for 211 inside 47 overs, while Morgan blazed 73 off 67 balls after England had been under some pressure in the run-chase.
Having bowled and fielded so well, the response from England’s top-order batsmen was underwhelming as they struggled to 64 for three after 18 overs.
Ian Bell promises so much at the top of the order with his clean strokeplay and he collected three boundaries in the second over of the innings, bowled by Lonwabo Tsotsobe.
But the extra pace of Dale Steyn proved a different matter and Bell was trapped lbw in the third over for 12.
The departure of the quick-scoring Bell was obviously a major early boost for South Africa and the superb work of the back-up pacemen – Morne Morkel and Wayne Parnell – as well as spinner Robin Peterson ensured that the more obdurate qualities of Alastair Cook (20 off 47 balls) and Trott were the ones that shone through.
Cook, pulling a Peterson short ball straight to deep midwicket, and Ravi Bopara, given out caught behind off Morne Morkel for a duck, were both unhappy with their dismissals but Morgan then came in and took charge with an innings of enormous authority.
Whatever stroke he played, whether orthodox or innovative, he committed to it fully. The left-hander purred along to his half-century off just 54 balls, with five fours and a six.
The jury may still be out on Trott as a limited-overs player, but the truth is that his was a vital innings in the circumstances for England.
The South African-born batsman committed himself to being the sheet-anchor, turning over the strike for Morgan to make merry.
At one stage South Africa had a sniff, but after Morgan and Trott had added 108 off 119 balls, England were firmly in control.
Morgan hits the ball so cleanly, collecting seven fours and two sixes in his innings, that it was a major surprise when the ball skewed straight upwards from an attempted sweep, presenting Peterson with an easy return catch. It’s perhaps worth reminding Peterson of how Herschelle Gibbs cost South Africa dearly at the 1999 World Cup by celebrating a catch too early, because the left-arm spinner lost the ball before throwing it up, but fortunately the umpires ruled he had completed the catch.
South Africa were still fighting hard and Craig Kieswetter was run out for 14 as he responded slowly to a quick single called by Trott and was beaten by Parnell’s fine piece of fielding.
Trott fell just five runs from victory when Parnell had him caught behind off 71 off 125 balls, with just two fours, but allegations that he had not served his team superbly were well wide of the mark.
South Africa’s bowling – Tsotsobe apart – was impressive.
Morkel barged in with typical aggression and showed good control as he took one for 41 in his 10 overs, while Parnell was excellent despite not swinging the ball back into the batsman, finishing with one for 23 in 10 overs.
Peterson also did his best to bowl South Africa back into the game, taking two for 39, while Steyn, having missed the first two ODIs with a neck injury, did not fully hit his stride and took one for 32 in seven overs.
Tsotsobe was the major disappointment. The slow pitch, which gripped, should have suited the pace at which he bowls as well as the cutters he is normally so good at bowling. But the left-arm seamer was flogged for 55 runs in seven overs.
England’s bowlers had earlier pressured and frustrated the South African batsmen, leading to rash strokes.
Pacemen Dernbach (9-0-44-3) and Jimmy Anderson (9.4-0-44-4) led the way for England but, on a slow pitch, medium-pacer Bopara (10-1-31-1) and off-spinner James Tredwell (10-0-49-2) also played key roles as South Africa were bowled out in 46.4 overs.
South Africa had won the toss and elected to bat, and openers Hashim Amla and Graeme Smith breezed to 50 off 51 balls before the tourists’ momentum was arrested by a rash stroke by Smith.
Looking to impose himself (unnecessarily with things going so well), Smith came down the pitch to Anderson and then, when the bowler pitched short, he was forced to try and pull the ball, missed and was bowled for 18.
Amla once again played some superb strokes, although he did not always get reward for them as he picked out the fielders, going to a nifty 43 off 51 balls and collecting five fours before Dernbach, born in Johannesburg and educated at St John’s, removed him with the first ball of his second spell as he returned for the bowling powerplay.
Amla drove loosely and did not move his feet at a delivery that nipped back and found the inside-edge and then went on to the stumps.
Dean Elgar and AB de Villiers then added 47 for the third wicket in nine overs before the South African captain tried to get too clever.
Tredwell is not the most threatening off-spinner on the planet and the plan had obviously been hatched to target the inexperienced Kent man. Between them, De Villiers and Elgar came down the pitch three times in his previous over, which cost 13 runs.
De Villiers was down the wicket again to the second delivery of Tredwell’s next over, but this time it was a straighter delivery, he was not quite to the pitch, but he went through with the shot and was caught at long-on for 28.
For such a quality batsman, never mind the captain, it was shoddy batting and a gift of a wicket to England.
Faf du Plessis (1) then stepped across outside off stump to expose his leg stump and was bowled by Bopara as South Africa crashed to 122 for four.
Elgar continued to soldier on, his 42 off 61 balls showing the fighting qualities of the left-hander, before the wonderful skills of Dernbach claimed his wicket.
The change of pace and the accuracy of Dernbach’s back-of-the-hand slower ball are remarkable and Elgar was left groping as he was bowled through the gate in the 31st over.
With Dale Steyn returning in place of all-rounder Ryan McLaren, South Africa’s batting had obviously been weakened and the new number one-ranked team were grateful for the grit of the left-handers, JP Duminy and Robin Peterson, that at least assured they had something to bowl at.
Dernbach found the edge of Parnell’s bat twice, conceding three boundaries in the 33rd over, before the left-hander edged another ball that seamed across him to the wicketkeeper.
Duminy and Peterson put on 40 for the seventh wicket before Duminy also tried to lay down the law to Tredwell and holed out to long-off. In a way, his dismissal was even more frustrating because he had shown such good composure in scoring 33 before throwing it all away in the 42nd over.
Even though Peterson survived through to the end of the innings, he could only collect one boundary and score 23 not out off 35 balls.
Anderson was the most successful of the England attack, bowling Dale Steyn (1) and Morne Morkel (7), before trapping Lonwabo Tsotsobe lbw for a first-ball duck, but at that stage the damage had already been done.
This was mainly due to Dernbach’s wonderful bowling in the middle of the innings, while Bopara and Tredwell also proved far trickier to hit than the South Africans had perhaps thought.