The former Arsenal duo scored within the space of 10 first-half minutes in between two reds cards awarded to Sporting's Ricardo Esgaio and Pedro Goncalves.
After securing a 4-1 win at home against Sporting in the reverse fixture last week, the Ligue 1 outfit enjoyed more success against their Portuguese counterparts, and tonight's victory has seen them climb up to second place in Group D.
Ruben Amorim's side have slipped down to third place but they are level on points with Marseille, while Tottenham Hotspur have moved to the summit of the group courtesy of a 3-2 home win against Eintracht Frankfurt.
After a relatively reserved start to the contest, Marseille were awarded a penalty in the 17th minute when Esgiao brought down Amine Harit inside the area, with the Sporting wing-back subsequently shown a second yellow card after being booked only three minutes earlier for a late tackle.
Guendouzi stepped up to score his first ever Champions League goal, striking the ball in off the post beyond Sporting goalkeeper Franco Israel.
Marseille then doubled their lead on the half-hour mark when Harit received the ball on the right and teed up Sanchez to tap in from just a few yards out - the Chilean was initially adjudged to be in an offside position but the goal was awarded following a VAR review.
Amorim made three substitutions before the half-time whistle in an attempt to restore something from the game with 10 men, but they struggled to pose a real threat to Marseille's backline.
Sporting had a huge mountain to climb in the second 45, and their night went from bad to worse on the hour mark as Pedro Goncalves was shown two yellow cards within a matter of seconds - his first for a late challenge on Leonardo Balerdi before needlessly receiving his second for his reaction towards the referee.
Marseille's supporters were unable to celebrate last week's win over Sporting as the match in the South of France was played behind closed doors, but they were heard loud and clear in the away end of the Estadio Jose Alvalade this evening as they watched their side see out a comfortable victory.
Igor Tudor's side will book their place in the Champions League last 16 if they beat Frankfurt in their penultimate Group D fixture in two weeks' time, and if Spurs secure maximum points against Sporting.