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.
Cardiff's preparations took an unconvincing turn as they let a two-goal lead slip to lose 3-2 at Brentford.
Kim Bo-kyung put Cardiff ahead 12 minutes in after exchanging passes with Fraizer Campbell, who doubled the Bluebirds' lead two minutes later.
But Conor McAleny's neat finish cut the deficit just before half-time and the on-loan Everton forward equalised four minutes into the second period before Paul Hayes' scrappy late goal earned Brentford victory.
Norwich were held to a 1-1 draw at Brighton in front of an impressive crowd of 10,622 at the Amex Stadium.
Jonny Howson turned home Nathan Redmond's cross in the 27th minute and Andrea Orlandi missed a clear chance for a Brighton equaliser just before the break.