The two forwards did a fine job making sure the Colombia international was not missed as Les Rouge et Blanc took full advantage of their title rivals' draw at Guingamp.
Germain opened the scoring just before the interval with a composed finish before strike partner Riviere smashed home 12 minutes into the second half to seal victory for the hosts.
Monaco's staff and players may have still been reeling from the news that star striker Falcao will miss the rest of the season with a crucial ligament injury, but it certainly didn't show in early exchanges as they set about attempting to take full advantage of PSG's surprise draw at Guingamp the day before.
Indeed, Les Rouge et Blanc made a blistering start to the game and really could have been a couple of goals to the good before the close of the opening quarter.
However, Steve Mandanda was in inspired form for the visitors. The Marseille goalkeeper was called into action for the first time after fewer than 60 seconds of action when Andrea Raggi picked out Emmanuel Riviere unmarked in the area with a wonderfully measured ball from the right wing. Unfortunately for the hosts, though, Mandanda pulled off a spectacular, one-handed save to deny the Monaco forward.
The France international pulled off another terrific stop moments later, after the ball had rolled invitingly into the path of Raggi on the edge of the Marseille box.
Monaco, though, really should have taken the lead 18 minutes in when some dreadful clumsy defending from Souleymane Diawara allowed Riviere to charge through on goal. However, while the 23-year-old attacker sent Mandanda the wrong way, he dragged his shot wide of the left post.
It seemed as if Monaco, for all its dominance, was going to go in scoreless at the break only for Germain to make the breakthrough on 41 minutes, just when Marseille was actually starting to gain a foothold in the game.
Joao Moutinho was the creator, picking out Germain, who escaped the attention of the hapless Diawara before coolly slotting the ball home to give the home side a deserved lead.
Monaco doubled its advantage just more than 10 minutes into the second half when Riviere, who appeared to have been ever so slightly offside, controlled a brilliant ball from Geoffrey Kondogbia with the outside of his right foot before smashing it into the roof of the net.
Marseille had a wonderful opportunity to immediately halve the deficit when Andre-Pierre Gignac barged his way into the area, but his effort was brilliantly blocked by Danijel Subasic.
The visitors never looked remotely capable of turning the game around after that, as Monaco coasted to a win that drags it right back into the title race.