Charlie Adam struck a hat-trick and Makhtar N'Diaye could also have forced himself into new Rangers manager Paul Le Guen's first-team plans.
St Mirren had hoped to have Charlie Adam back this season
Senegal midfielder N'Diaye played in a 4-0 defeat of a Jomo Select in South Africa, after which Le Guen said: "It is possible he could win a contract."
The 20-year-old Adam, who was on loan to St Mirren last term, was star man.
"I was very pleased with him and his goals. He can be a part of my squad for sure," said Le Guen.
"I know he was on loan last season, but he has talent and he has worked very hard."
Adam's performance will be bad news for St Mirren, who had been hoping to re-sign the midfielder after he helped them win promotion to the Scottish Premier League.
I was happy with the new players
Rangers manager Paul Le Guen
Le Guen fielded a mix of young players and new signings for a match, played behind closed doors, in which Rangers were rarely tested.
Summer arrivals Libor Sionko, Karl Svensson, Jeremy Clement and goalkeeper Lionel Letizi all started the match, although the three outfield players were rested for the second period.
The 24-year-old N'Diaye, who is on trial after leaving Rennes, played alongide Clement in central midfield.
"Overall, I felt it was a good performance from the players," said Le Guen. "They all did well.
"I was happy with the new players. I knew they would be fine because they are sharp and fit."
Nacho Novo set up Adam for the opener with a fine through ball after 10 minutes at the Boksburg Stadium.
And the pair combined again for the second two minutes later.
Adam latched on to an Ian Murray back-heel to add the third in the second half.
Striker Kris Boyd, who had replaced new signing William Stanger on the hour mark, added a fourth for the Glasgow club.