Two tries in the space of 10 minutes from back row man Louis Madaule enabled the French to pick up a second bonus point as they reached the four try mark 10 minutes into the second half, ultimately finishing 32-14 winners.
It means the big clash in Swansea on Saturday afternoon will be a winner-takes-all occasion with the triumphant side moving into a semi-final showdown with the winners of Pool A. Wales also picked up a bonus point in beating Japan 33-10.
That team will be decided when the Pumitas, Argentina's youngsters, meet the reigning IRB World U19 champions New Zealand at the weekend.
Having overcome Ireland 17-9 on Day 1, the Pumitas had outside half Benjamín Madero to thank for their bonus point, 30-10 victory over Tonga. He scored 15 points as he went through the card with a try, two conversions, penalty and drop goal.
The young All Blacks were flying high at half-time in their late kick-off against the Irish, having notched a bonus points with four first-half tries to lead 34-3.
In Pool B, the Samoans underlined their step-up in class with a second victory to put them in line for a crack at the high scoring South Africans in Wrexham on Saturday.
Having beaten the Scots on the opening night of the global U20 tournament the Pacific Islanders picked up another scalp at The Racecourse by beating the USA 20-6. If it was a much improved result for the Americans - they shipped 16 tries and 108 points against South Africa on opening night - it was another fine performance from the Samoans, who only led 7-6 at the break.
The Springboks, meanwhile, added another 10 tries to their collection with a 72-3 hammering of Scotland. There were 22 points for outside half Francois Brummer to take his tournament tally to 40.
In Pool C, the Six Nations U20 Grand Slammers, England, ran over Canada 60-18 with a nine try haul. Outside half Rob Miller got one of them and ended with 20 points.
England will now face Australia at Rodney Parade on Saturday in the match that will decide who meets either South Africa or Samoa in the semi-finals.
The Wallabies beat Fiji 53-17 to maintain their 100 per cent record in the tournament. They picked up nine tries, with the first two going to left wing Junior Sovala Futi.