Lee Martin marked his call-up to the Manchester United first team by scoring the winner in this Vodacom Challenge match.
The midfielder, on loan at Sheffield United last season, found the target at the Absa Stadium in the 23rd minute.
Martin reacted quickly after Fraizer Campbell flicked the ball on, the 21-year-old applying a cool finish.
It was no more than United deserved against an enthusiastic but limited Pirates side, coached by former Dutch star Rudi Krol.
Manager Sir Alex Ferguson named a young team with Wayne Rooney, Ryan Giggs, Gary Neville, Paul Scholes and Nemanja Vidic all on the bench.
And the Scot would no doubt have been pleased at the way his side applied themselves against a fired-up Pirates team.
Wes Brown was in from the start but is scheduled to return home tomorrow after the death of his pregnant half-sister.
Rio Ferdinand captained the team after recovering from a back problem that forced him to miss the draw against the Kaizer Chiefs at the weekend.
United almost made the breakthrough in the seventh minute when Carlos Tevez turned quickly, only to see his effort turned away by Senzo Meyiwa.
The goalkeeper was forced to make another good save three minutes later from Lee Martin.
Then Michael Carrick, back after a slight hamstring injury, rattled in shot that was deflected to safety.
Campbell, who scored 15 goals while on loan at Hull last season, set up United's goal.
He flicked on a pass from Brown and Martin made no mistake from an acute angle.
Carlos Tevez almost extended their lead in the 34th minute when he made space on the edge of the area but failed to test the goalkeeper.
The Pirates were playing with no lack of enthusiasm in front of a passionate crowd but found the opposition hard to break down as half-time approached.
Ferdinand was then booked in the 40th minute by referee Cornelius Mwanza after believing United should have had a penalty when Martin went to ground.
The Pirates tried to set the tempo at the start of the second half but they struggled to string their passes together.
Goalkeeper Ben Foster was tested for the first time in 65th minute when he did well to push over a shot from Lebogang Mothibantwa.
Scholes and Rooney were then introduced, replacing Tevez and Michael Carrick in the 69th minute.
Rooney was quickly into the action and released Campbell four minutes later but he was crowded out.
Then Scholes rattled in a shot from the edge of the area but the goalkeeper was equal to it and made a good block.
The Pirates hit back, however in the 79th minute and Foster made a point-blank save from Joseph Makhanya.
United have now picked up four points in the tournament and will have their final game in Pretoria on Saturday.
They will face either the Pirates or the Chiefs, who meet on Thursday in Port Elizabeth.
Sir Alex Ferguson believes Ben Foster can become England's first-choice goalkeeper now he has fully recovered from a knee operation.
The 24-year-old was impressive in the 1-0 victory against Orlando Pirates tonight in the Vodacom Challenge match in South Africa.
Ferguson said: 'I still believe Ben will be England's goalkeeper for the next few years.
'We did not expect him to get fit so quickly last season and I did not include him in our European squad.
'When I saw his performance against Derby there was maybe some regret on my part.
'The ability he has he is going to be challenging for a first-team place next season. That can only be good news for England.
'With an experienced goalkeeper like David James coming back in the squad it tells you there is an opportunity for someone like Ben.'
However, Ferguson confirmed that Van der Sar would be his number one next season.
'It will be difficult for Ben only because he is in competition with one of the best goalkeepers of all time, ' said the United boss.
'Edwin is a man of great experience and consistency and has looked after himself so well.
'He can play until he is 40. Ben is 24, so can play for the next 14 to 15 years. There is no need for the boy to panic. His time will come.'
Ferguson added: 'I thought we played well in the first 25 minutes but it sometimes happens to young players, they lose their concentration.
'In the second half when Wayne Rooney and Paul Scholes came on we started to get our composure back a little bit.
'But the Pirates played with fantastic aggression. They had speed up front, which caused us bother at times. We were a bit lucky we did not lose a goal.'