The Lions followed their victories over the Barbarians and Western Force with a 22-12 victory at the Suncorp Stadium in their toughest test of the tour so far.
Leicester Tigers scrum-half Youngs, who made his first start of the tour, forced the Reds No8 Jake Schatz and scrum-half Nick Frisby into a mistake at a defensive scrum in the 34th minute and capitalised with a simple score.
The try gave the Lions an 11-7 lead after they had trailed to an individual try by Australia international wing Luke Morahan. Youngs’ effort was converted by Owen Farrell, who also kicked three first-half penalties for the Lions as they led 16-9 at the break.
Frisby crossed for a second score for the Reds in the second period but two more penalties for Farrell saw The Lions home.
Youngs was one of four Tigers to start the game. His brother Tom played 64 minutes on his first start of the tour after replacement appearances in the first two games.
Geoff Parling made his first of the tour and played the whole 80 minutes in the second row while Manu Tuilagi, making his second start, was replaced by George North in the 20th minute after receiving a knock to his shoulder.
Dan Cole came off the bench as a 64th-minute replacement for Mako Vunipola on the loosehead side of the scrum.
The Tigers and England prop will start on his favoured tighthead side for the Lions when they face the Combined Country XV in Newcastle, New South Wales in their next tour match on Tuesday (kick-off 10.30am BST live on Sky Sports 2).
Logovi’i Mulipola won his 11th international cap as Samoa recorded a first ever victory over Scotland in the ninth meeting between the countries.
Samoa outscored Scotland by three tries to one with former Tigers winger Alesana Tuilagi collecting two of them.
Tigers Academy product Greig Tonks, now of Edinburgh Rugby, won his first cap in the game in Durban, which was the opening fixture of a quadrangular tournament which also involves South Africa and Italy. The hosts ran out 44-10 winners against the Azzurri, for whom Martin Castrogiovanni was on the bench.
Niall Morris, meanwhile, made his first start for Emerging Ireland as they came through a tough clash with Georgia in their opening fixture of the IRB Tbilisi Cup.
Morris played the full 80 minutes as two late penalties for Ian Keatley saw Emerging Ireland secure a 20-15 over the hosts at Avchala Stadium.
