The 19-year-old, who booked his place through local final qualifying at nearby North Berwick, is more concerned with not making a mess of his first tee shot.
By virtue of his surname, Mullen has been posted close to two alphabetically-similar multiple major winners in the Muirfield locker room but he is not yet grown accustomed to being treated like one of the professionals.
"My locker is right next to Mickelson's being an M and I'm thinking 'Bloody hell, he's got the same little locker as me'. It's brilliant," he told Press Association Sport.
"I came up early to get the nerves out of the way and I got to play with Martin Kaymer and Jason Duffner and that settled me down really well.
"When I played with them I was really nervous to start off with but after I hit a good shot that settled me down and then I played with Ben Curtis (2003 Open champion) and Freddie Jacobsen and I wasn't nervous at all.
"I have to worry more about what I am doing than who everyone else is and I just need to get off to a steady start and I think I'll be all right.
"But my first thought on the first tee on Thursday will be 'Find the clubhead' and hopefully I can make par."
The North Devon Club amateur has been drawn with fellow qualifiers Steve Tiley, from Kent, and American Josh Teater.
It is not the group he wanted but Mullen is just happy to be in the field.
"I was most looking forward to seeing who I would be playing with in the first two rounds - I would have picked Tiger because he is a different guy altogether," he added.
"I'll need to play well over two days to stand any chance of playing with him because there's only one place he will be and that is near the top of the leaderboard.
"Obviously you want to play with the higher-profile players but I'll be under the radar because I'm not playing with superstar names."