Morgan has been an integral figure in England's rise to No. 1 in the International Cricket Council's ODI rankings, and is leading the home team at the 12th World Cup.
The 32-year-old left-hander made his international debut for Ireland in 2006 but gained selection for England in 2009 and has helped transform the English lineup into an attacking unit since its group-stage exit at the 2015 World Cup in Australia.
After being sent into bat by South Africa, England was 107-2 when Morgan went to the crease in the opening game of the tournament at the Oval.
South Africa legspinner Imran Tahir has dismissed England opener Jonny Bairstow with the second ball of the World Cup.
After winning the toss and electing to bowl, Tahir was a surprise pick to bowl the first over of the tournament opener.
He conceded a single to Jason Roy with the first ball and then had Bairstow caught behind off a faint edge the very next ball as World Cup favorite England slipped to 1-1.
South Africa captain Faf du Plessis has won the toss and sent England into bat in the opening game of the Cricket World Cup.
No. 1-ranked England is the favorite to win the title on home soil, and its vaunted top order will be in action immediately as the tournament opens at the Oval in south London.
Pace bowler Jofra Archer was selected to make his World Cup debut for England.
Lineups: England: Jonny Bairstow, Jason Roy, Joe Root, Eoin Morgan (captain), Jos Buttler, Ben Stokes, Moeen Ali, Chris Woakes, Adil Rashid, Liam Plunkett, Jofra Archer.
South Africa: Hashim Amla, Quinton De Kock, Aiden Markram, Faf du Plessis (captain), Rassie van der Dussen, JP Duminy, Dwaine Pretorius, Andile Phehlukwayo, Kagiso Rabada, Lungi Ngidi, Imran Tahir.
England and South Africa meet in the opening match of the 12th Cricket World Cup on what should be a bowl-first pitch at the Oval on Thursday.
England brings outstanding form from the last four years, including a 4-0 sweep of Pakistan in a one-day international series this month. The home side is the hot favorite to win its first World Cup title.
South Africa was also impressive in its most recent ODI series, a 5-0 rout of Sri Lanka at home in March. But the Proteas come in under the radar.
England picked its lineup on Wednesday without revealing it to the public, leaving in doubt whether its fastest bowler, Mark Wood, will play after he injured his left ankle on the weekend.
South Africa is without veteran paceman Dale Steyn, but fellow fast bowlers Kagiso Rabada and Lungi Ngidi have recovered from their own recent injuries and are expected to play.