Despite ending up on the losing side, Warriors wing Alex Grove also caught the eye for Scotland after being handed a starting spot.
The four home nations, Scotland, England, Ireland and Wales, are fielding Under-20 teams in this year's Under-21 Six Nations Championship, whilst France and Italy will field Under-21 sides.
And Academy boss Stanley and assistant Gary Meechan were delighted that the Worcester trio featured so prominently on the international stage after already showing good form in Sixways Academy and Guinness 'A' League matches this season.
"Matt Mullan had a very strong game in his role as hooker, the lineout operated very smoothly. Matt's presence in the scrum and particularly in loose play was also very pleasing to watch," said Stan, who travelled to watch the game at The Rec.
"Matt Cox came on as a blood replacement and went on to play the remainder of the game. To come away with scoring two tries was very good from his point of view too.
"And Alex Grove, although under a lot of pressure in defence, was very effective and had a very solid game with the amount of work he had to do.
"From our point of view, to get all three out on the pitch was very rewarding and reflects well on what we're doing here at Sixways."
Mullan and Cox were also in action as England made it two wins out of two by piling up a four-try 30-10 victory over Italy Under-21s at The Rec the following weekend.
Front row Mullan played the opening 53 minutes as hooker and Cox came off the bench to make sure victory was secured.
England are next in action against Ireland U20s at Atlone on February 23, before they face France Under-21s at Northampton on March 9 and finish with Wales Under-20s at Newport on March 16.