Marseille, still reeling from the shock resignation of coach Marcelo Bielsa following their opening 1-0 defeat to Caen, failed to threaten the Champagne side who won their opening two matches of the season for the first time since returning to the elite four years ago.
"It's satisfying to achieve another win against a big team after Bordeaux," said Reims coach Olivier Guegan, whose side provisionally take top spot equal on six points with Caen, 1-0 winners on Saturday against Toulouse, and ahead of Sunday's later games when champions Paris Saint-Germain are at home to newly-promoted Corsican minnows Gazelec Ajaccio.
"We got our own back for the blow last year," added Guegan, whose side lost 5-0 at home to Marseille last season.
"The team were organised, disciplined and structured, but we have to keep our feet on the ground, there's a long way to go."
Bielsa's assistant Franck Passi took charge in Reims but insisted the Argentine's departure could not be used as an excuse as Marseille lie in the relegation zone.
"We have to stop talking about trauma! We've put last Sunday (Bielsa's resignaton) behind us," said Passi.
"We mustn't hide behind that excuse. But it's clear that it will not be easy and it will take time to find a solution."
Marseille's forward line of Michy Batshuayi, Florian Thauvin, Romain Alessandrini and Lucas Ocampos rarely threatened Reims goalkeeper Kossi Agassa.
Winger Alessandrini got a rare chance after 12 minutes but fired over only for Reims to break the deadlock two minutes later, Mali defender Traore volleying low into the net after Benjamin Mendy had headed away a corner.
Shaken Marseille paid for their lack of precision and rarely threatened Agassa, while by contrast Reims could have added to their tally but for some fine goalkeeping by OM captain Steve Mandanda.
Mandanda, who was making his 300th Ligue 1 appearance, did well to keep out another Traore effort on 29 minutes and David N'Gog's shot on 61.
Marseille will be desperate for a win next Sunday at home against newly-promoted Troyes, who came from behind to claim their second consecutive draw with a 3-3 stalemate at home against Nice on Saturday.
Passi added: "There has only been two matches, there's a long way to go. I'm not feeling any particular pressure. We're just going to get back to work."