Fabio Capello's side made a dream start at the Royal Bafokeng Stadium in Rustenburg when captain Steven Gerrard gave them an early lead in the Group C clash.
They looked good value for their lead but United States were level before half-time when Clint Dempsey's tame shot slipped through Green's hands.
Green had been chosen ahead of David James and Joe Hart after Capello kept his squad guessing over the starting line-up until two hours before kick-off.
Bob Bradley, meanwhile, was able to start Jozy Altidore after the striker overcame an ankle complaint - but USA were unable to attack in the early stages as England got off to a perfect start.
Capello's side were ahead in the fourth minute through Gerrard, who was given the armband following Rio Ferdinand's knee injury that has ruled him out for the tournament.
The move started with Glen Johnson's throw and Frank Lampard prodding the ball inside towards the edge of the penalty area. Emile Heskey flicked the ball forward for Gerrard to race through and finish beyond Tim Howard.
It was Heskey's first start in any game since March but he provided an all-round performance that justified his inclusion.
United States struggled to get to grips with the game but created half chances with headers from Dempsey and Oguchi Onyewu, although neither efforts tested Green.
Altidore had their first genuine sight of goal when Landon Donovan crossed and found him unmarked but the striker's header went wide.
They were gifted their equaliser five minutes before the break through Green's mistake.
Dempsey spun around Gerrard 30 yards from goal but there seemed little danger when he unleashed a shot that lacked power and was heading straight to Green.
The West Ham goalkeeper looked to have it covered but it squirmed out of his grasp and over the line.
In the second half, Heskey had a chance to add to his seven international goals when Aaron Lennon sent him through but the Aston Villa striker saw his finish saved.
Green made up for his mistake in the 65th minute when Altidore raced around Jamie Carragher and had a shot tipped onto the post.
England (4-4-2): Green; Johnson, King (Carragher 46), Terry, A Cole; Lennon, Gerrard, Lampard, Milner (Wright-Phillips 31); Heskey (Crouch 79), Rooney.
Subs (not used): James, Hart, Dawson, Warnock, Upson, J Cole, Barry, carrick, Defoe.
United States (4-4-2): Howard; Cherundolo, DeMerit, Onyewu, Bocanegra; Dempsey, Bradley, Clark, Donovan; Findley (Buddle 77), Altidore (Holden 86).
Subs (not used): Guzan, Hahnemann, Spector, Bornstein, Goodson, Beasley, Torres, Edu, Feilhaber, Gomez.