Eoin Morgan played a pivotal role as England beat South Africa
Having lost the Test series 2-0 and fallen 1-0 behind after two matches of the one-day leg, England turned the tide at the Kia Oval courtesy of Morgan's fluent 73 and a stoic 71 from Trott.
The bowlers played their part by dismissing the tourists for 211, Ravi Bopara miserly with one wicket for 31 runs in 10 overs and James Anderson polishing off the tail to close with four for 44.
England briefly looked in bother on 64 for three but Trott played the anchor role in a dogged 125-ball innings, while Morgan added the flair with seven fours and two sixes.
Ian Bell wasted no time getting England's chase going but, after crashing three boundaries in Lonwabo Tsotsobe's first over, he was pinned leg before wicket by Dale Steyn.
His opening partner Alastair Cook took 18 balls to get off the mark and was particularly sedate and went for a laboured 20 with a tame shot to Robin Peterson.
Bopara then fell for a disputed duck, given caught behind off Morne Morkel but Morgan's arrival added much-needed impetus - not to mention boundaries - as he raced past 30 at better than a run-a-ball.
Morgan's game-changing knock ended with a looping caught-and-bowled to Peterson and 40 still needed.
Craig Kieswetter cleared the ropes once before being run out for 14, leaving Trott to shepherd England within five runs of victory. The impressive Parnell accounted for the number three, via the outside edge, but Samit Patel was on hand to hit the winning boundary.
Jade Dernbach offered support to Anderson with three for 44 and the in-form Hashim Amla top-scored with 43 for the Proteas.