The devout Muslim was made to train on his own earlier this month after claiming he could not wear a shirt featuring the logo of the pay-day lenders, who sponsor the Magpies.
But after a settlement was reached Cisse returned to action in Paisley and swept home the opener in a comfortable 2-0 win for the visitors.
There was warm applause for United's Paul Dummett and Conor Newton from the home support after the duo helped the Buddies lift the Scottish Communities League Cup during loan stints last term, while the crowd of 4,216 featured 709 travelling Newcastle fans.
Cisse put the visitors ahead when he exchanged passes with Sammy Ameobi and curled a well-placed finish into the top corner after 18 minutes.
Saints number one David Cornell was forced to dive full length to save Dan Gosling's header from Ameobi's dinked cross soon after.
However, the keeper had no chance as full-back Matthew Debuchy slotted a composed finish on 26 minutes after Vurnon Anita sent him racing through on goal.
Premier League new boys Cardiff City went down to a shock 3-2 defeat against Brentford at Griffin Park - after going two goals up.
A Kim Bo-Kyung header began the scoring before Fraizer Campbell made it two inside the opening quarter of an hour from a square Kim pass.
On-loan Everton forward Conor McAleny fired home before the break to get Brentford back in it then scored an almost identical drive two minutes into the second period to draw them level.
Substitute Paul Hayes scored the winner at the death.
The other Premier League side in action, Norwich City, were held 1-1 at Brighton.
British friendly results
St. Mirren 0 - 2 Newcastle United
Brentford 3 - 2 Cardiff
Brighton 1 - 1 Norwich
Northampton 2 - 1 Leicester
Maidenhead U 4 - 2 Gillingham
Aveley 3 - 1 Dag and Red
Kidderminster 3 - 1 Cheltenham
Gainsborough 0 - 5 Mansfield
Stalybridge 2 - 2 Accrington