The full-back became the second Uruguayan (after Diego Forlan) to represent the club as he made his senior debut as a second-half substitute against West Ham at Old Trafford.
Varela was given his opportunity as Paddy McNair added to United's somewhat lengthy injury list and lined up at right-back, showing a willingness to go forward but also getting stuck in with a number of important blocks and challenges in his 45-minute cameo.
With United's backline weakened by injures to Marcos Rojo, Phil Jones, Luke Shaw and Antonio Valencia, Varela became the latest young talent to be promoted from the Reserves into the senior side (Cameron Borthwick-Jackson, Axel Tuanzebe, Sean Goss and Marcus Rashford have all featured on a first-team bench this season)
"He's been playing well for the Under-21s and he's got the talent, today has been the first little indication that maybe he will get more chances in the first team"
Varela was brought to United in 2013, becoming the first player to be signed by David Moyes in his ill-fated tenure as boss having impressed for Uruguay in the Under 20 World Championships, for a fee of around £5m.
After catching the eye in an impressive stint with Castilla, he was even included in Real Madrid's Champions League squad last term.
He will hope to build on his first 45 minutes for United and could be in contention to make the flight to Wolfsburg on Monday ahead of the do-or-die clash in Germany on Tuesday.