Youngs made a trademark break off the back of a lineout after a pass of the top by his Leicester Tigers teammate Tom Croft.
The Tigers scrum-half, who came on as a 60th minute replacement, held off a couple of attempted tackles before his momentum took him under the posts for the Lions' fifth and final try of the game.
It was Youngs' second try of the tour after his score against the Queensland Reds and helped the Lions to a convincing win against their Super 15 opponents.
Manu Tuilagi played the full 80 minutes on his return from a shoulder injury, Dan Cole played the first 50 minutes and Croft came on for the final 15 minutes.
Good work by Cole at a 5m scrum took the Lions up to the line where Conor Murray turned out of a couple of tackles to dive over. Farrell added a touchline conversion from the right to give the tourists a 7-0 lead.
Tuilagi was heavily involved in the second try. His break on to Sean O’Brien’s inside pass took the Lions deep into Rebels territory, Maitland took up the charge but the chance looked to have gone when Faletau slipped just short of the line. However, they secured possession for Maitland to rejoin the attack and score on the right. Farrell added the extras to give the Lions a 14-0 lead at half-time.
The tourists extended the lead with a neat lineout move nine minutes after the break. Faletau collected clean ball and set it up for Richie Gray and Dan Lydiate before O’Brien added the finish from close range. Farrell made it three from three with the conversion.
The lineout was the source for the Lions’ fourth with 20 minutes left. Replacement hooker Rory Best was tackled from an offside position as the Lions’ drive looked set to score and referee Glen Jackson awarded the penalty try. Stuart Hogg, on as a replacement, took over the kicking duties and landed the conversion.
And it was from another lineout that the Lions scored their fifth and final try. Croft’s pass off the top was collected by Youngs, who darted through a gap and rode a couple of tackles to score under the posts.
The Lions face Australia in the second Test on Saturday in Melbourne (kick-off 11.05am BST).
