Davies, the late try hero in the epic late win over champions Toulon in Round 2, comes into the starting line-up as Director of Rugby Phil Davies makes just one chance to his side.
Rhys Patchell, who scored a try in the closely fought 29-20 win when the teams met last week at the Arms Park, moves to inside centre with Dafydd Hewitt (shoulder) ruled out.
Lock James Down and back row Andries Pretorius are called onto the replacements bench.
Davies said: “We were pleased with the motivation and spirit we showed last week. We have been getting better all year and at moment the performance levels are growing.
“We will need to work even harder up in Scotland. We need to go up level physically and tactically, be more accurate with the ball. Last week was about desire and performance, this week we need to extract even more from the players.
“I expect Glasgow to play like men possessed,” he added. “We looked to play a certain way last week against them and executed it.
“But we know how good they can be and have had some terrific games up there. Friday will be no different.
“The team that controls the ball in the opposition attacking third will be hard to beat. It’s a tough game because they will have been disappointed by last week, but we need to build on what we have achieved in this competition.”
Cardiff Blues: 15 Leigh Halfpenny, 14 Alex Cuthbert, 13 Richard Smith, 12 Rhys Patchell, 11 Harry Robinson, 10 Gareth Davies, 9 Lloyd Williams; 1 Sam Hobbs (c), 2 Kristian Dacey, 3 Taufa’ao Filise, 4 Chris Dicomidis, 5 Filo Paulo, 6 Macauley Cook, 7 Rory Watts-Jones, 8 Robin Copeland.
Replacements: 16 Marc Breeze, 17 Thomas Davies, 18 Benoit Bourrust, 19 James Down, 20 Ellis Jenkins, 21 Andries Pretorius, 22 Lewis Jones, 23 Dan Fish