They then travel to the Newport Gwent Dragons on New Year's Eve before rounding off a testing nine days with the visit of Zebre on Friday, January 4.
"We've got three tough games coming up and it's vital that we take something from each one of them," said Tandy, whose side have won six of their ten RaboDirect PRO12 games this season.
"We are still playing catch-up a little, because of the losses in the first three weekends and the good form of some of the other teams up near the top, so we can't afford anymore slip-ups.
"We know that the derby matches will be full-on, passionate affairs in front of big crowds and that's fantastic for the league and for the players, but we'll have to remain in control of our emotions and make sure we stick to the game plan if we are going to get our reward."
The Ospreys are the reigning RaboDirect PRO12 champions but lost their opening three games of the current campaign to Benetton Treviso, Ulster Rugby and Glasgow Warriors.
And with injuries to key players Tandy insists Ospreys will have to use their full squad if they are to continue their recent form, which has brought three victories in their last four outings.
"We've seen in recent weeks, with the injuries we've had, the quality of young players coming through here" said the 32-year-old former flanker.
"That's been a huge positive for us. Look at the teams that we fielded against Toulouse and you'll see plenty of local young talent, which is something we pride ourselves on as Ospreys.
"We are going to have to use the squad, change things about, over the next two weeks. We can't expect the same players to start every game, but we have faith in what we are doing here and what we've got available."
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