The Spanish duo will be glued to the Group B blockbuster in Gelsenkirchen between Spain and Italy, with qualification for the knockout stage at stake.
"21-3... to Spain" was two-time F1 world champion Alonso's 'cautious' prediction of the outcome, delivered with only the merest hint of a smile.
His fellow countryman Sainz was more circumspect, possibly because as a Ferrari driver he has to live and work and breath all things Italian.
"It's going to be fun to watch surrounded by Italians," said Sainz. "I think we will win 2-1 with a late goal for Spain."
The meeting between the reigning European champions Italy and three-time former winners Spain is the standout tie of the opening round at the tournament.
Top spot in Group B, and a theoretically easier last-16 draw, is at stake as Spain and Italy aim to build on victories in their opening matches against Croatia and Albania respectively.
