Eddie Howe handed non-competitive debuts to Nick Pope and Sven Botman during the 3-0 win over German third-tier side 1860 Munich on Friday afternoon.
Pope started in between the sticks, while Botman was introduced for the second-half after Jamaal Lascelles was withdrawn as a precaution.
Initially, Botman was due to play the final half-hour when Howe made 10 changes, which included Bruno Guimaraes, Kieran Trippier and Chris Wood.
Guimaraes scored one and assisted one inside the opening 17 minutes of him being on the pitch. Joe Willock and Sean Longstaff were also on the scoresheet.
Mainz make for a testing opponent at the Kufstein Arena after finishing 8th in the Bundesliga last term.
As ever, Howe will be looking to get the balance right in terms of minutes and a positive performance.
NewcastleWorld predicts the starting XI Howe will name to face Mainz 05:
1. GK: Martin Dubravka
Played the final half-hour against 1860 Munich as his battle with Nick Pope for the No.1 jersey continues.
2. RB: Kieran Trippier
Is set to add more minutes to the tank after playing 45 minutes against Gateshead and 30 versus 1860 Munich. Photo: Stu Forster
3. CB: Fabian Schar
A chance for Schar to play more minutes - and develop what could be an exciting partnership with Sven Botman. Photo: Ian MacNicol
4. CB: Sven Botman
Newcastle fans loved what they saw from their summer signing last time - and are desperate to see more.